qapi/migration.json | 107 +++++++++++++++++++++++++++++++------------- 1 file changed, 77 insertions(+), 30 deletions(-)
Rewrote calc-dirty-rate documentation. Briefly described
different modes of dirty page rate measurement. Added some
examples. Fixed obvious grammar errors.
Signed-off-by: Andrei Gudkov <gudkov.andrei@huawei.com>
---
qapi/migration.json | 107 +++++++++++++++++++++++++++++++-------------
1 file changed, 77 insertions(+), 30 deletions(-)
diff --git a/qapi/migration.json b/qapi/migration.json
index 179af0c4d8..19b51444b5 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -1735,14 +1735,14 @@
##
# @DirtyRateStatus:
#
-# An enumeration of dirtyrate status.
+# Dirty page rate measurement status.
#
-# @unstarted: the dirtyrate thread has not been started.
+# @unstarted: measuring thread has not been started yet
#
-# @measuring: the dirtyrate thread is measuring.
+# @measuring: measuring thread is running
#
-# @measured: the dirtyrate thread has measured and results are
-# available.
+# @measured: dirty page rate is measured and the results are
+# available
#
# Since: 5.2
##
@@ -1752,13 +1752,14 @@
##
# @DirtyRateMeasureMode:
#
-# An enumeration of mode of measuring dirtyrate.
+# Method used to measure dirty page rate. Differences between
+# available methods are explained in @calc-dirty-rate.
#
-# @page-sampling: calculate dirtyrate by sampling pages.
+# @page-sampling: use page sampling
#
-# @dirty-ring: calculate dirtyrate by dirty ring.
+# @dirty-ring: use dirty ring
#
-# @dirty-bitmap: calculate dirtyrate by dirty bitmap.
+# @dirty-bitmap: use dirty bitmap
#
# Since: 6.2
##
@@ -1768,26 +1769,25 @@
##
# @DirtyRateInfo:
#
-# Information about current dirty page rate of vm.
+# Information about measured dirty page rate.
#
# @dirty-rate: an estimate of the dirty page rate of the VM in units
-# of MB/s, present only when estimating the rate has completed.
+# of MiB/s. Value is present only when @status is 'measured'.
#
-# @status: status containing dirtyrate query status includes
-# 'unstarted' or 'measuring' or 'measured'
+# @status: current status of dirty page rate measurements
#
# @start-time: start time in units of second for calculation
#
-# @calc-time: time in units of second for sample dirty pages
+# @calc-time: time period in units of second for which dirty page
+# rate was measured
#
-# @sample-pages: page count per GB for sample dirty pages the default
-# value is 512 (since 6.1)
+# @sample-pages: number of sampled pages per each GiB of guest
+# memory. Value is valid only in page-sampling mode (Since 6.1)
#
-# @mode: mode containing method of calculate dirtyrate includes
-# 'page-sampling' and 'dirty-ring' (Since 6.2)
+# @mode: mode that was used to measure dirty page rate (Since 6.2)
#
-# @vcpu-dirty-rate: dirtyrate for each vcpu if dirty-ring mode
-# specified (Since 6.2)
+# @vcpu-dirty-rate: dirty rate for each vCPU if dirty-ring mode
+# was specified (Since 6.2)
#
# Since: 5.2
##
@@ -1803,15 +1803,50 @@
##
# @calc-dirty-rate:
#
-# start calculating dirty page rate for vm
-#
-# @calc-time: time in units of second for sample dirty pages
-#
-# @sample-pages: page count per GB for sample dirty pages the default
-# value is 512 (since 6.1)
-#
-# @mode: mechanism of calculating dirtyrate includes 'page-sampling'
-# and 'dirty-ring' (Since 6.1)
+# Starts measuring dirty page rate of the VM. Results can be
+# retrieved with @query-dirty-rate after measurements are completed.
+#
+# Dirty page rate is the number of pages changed in a given time
+# period expressed in MiB/s. The following methods of calculation
+# are available:
+#
+# 1. In page sampling mode, a random subset of pages are selected
+# and hashed twice: once in the beginning of measurement time
+# period, another one -- in the end. If two hashes for some page
+# are different, the page is counted as changed. Since this
+# method relies on sampling and hashing, calculated dirty page
+# rate is only the estimation of its true value. Setting
+# @sample-pages to higher value improves estimation quality but
+# at the cost of higher computational overhead.
+#
+# 2. Dirty bitmap mode captures writes to memory by temporarily
+# revoking write access to all pages and counting page faults.
+# Information about modified pages is collected into bitmap,
+# where each bit corresponds to one guest page. This mode
+# requires that KVM accelerator property "dirty-ring-size=N"
+# is *not* set.
+#
+# 3. Dirty ring mode is similar to dirty bitmap mode, but the
+# information about modified pages is collected into ring buffer.
+# This mode tracks page modification per each vCPU separately.
+# It requires that KVM accelerator property "dirty-ring-size=N"
+# is set.
+#
+# @calc-time: time period in units of second for which dirty page rate
+# is calculated. Note that larger @calc-time values will typically
+# result in smaller dirty page rates because page dirtying is a
+# one-time event. Once some page is counted as dirty during
+# @calc-time period, further writes to this page will not increase
+# dirty page rate anymore.
+#
+# @sample-pages: number of sampled pages per each GiB of guest memory.
+# Default value is 512. For 4KiB guest pages this corresponds to
+# sampling ratio of 0.2%. This argument is used only in page
+# sampling mode. (Since 6.1)
+#
+# @mode: mechanism for tracking dirty pages. Default value is
+# 'page-sampling'. Others are 'dirty-bitmap' and 'dirty-ring'.
+# (Since 6.1)
#
# Since: 5.2
#
@@ -1828,9 +1863,21 @@
##
# @query-dirty-rate:
#
-# query dirty page rate in units of MB/s for vm
+# Query results of the most recent invocation of @calc-dirty-rate.
#
# Since: 5.2
+#
+# Examples:
+#
+# 1. Measurement is in progress:
+#
+# <- {"status": "measuring", "sample-pages": 512,
+# "mode": "page-sampling", "start-time": 3665220, "calc-time": 10}
+#
+# 2. Measurement has been completed:
+#
+# <- {"status": "measured", "sample-pages": 512, "dirty-rate": 108,
+# "mode": "page-sampling", "start-time": 3665220, "calc-time": 10}
##
{ 'command': 'query-dirty-rate', 'returns': 'DirtyRateInfo' }
--
2.30.2Andrei Gudkov <gudkov.andrei@huawei.com> writes:
> Rewrote calc-dirty-rate documentation. Briefly described
> different modes of dirty page rate measurement. Added some
> examples. Fixed obvious grammar errors.
>
> Signed-off-by: Andrei Gudkov <gudkov.andrei@huawei.com>
> ---
> qapi/migration.json | 107 +++++++++++++++++++++++++++++++-------------
> 1 file changed, 77 insertions(+), 30 deletions(-)
>
> diff --git a/qapi/migration.json b/qapi/migration.json
> index 179af0c4d8..19b51444b5 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -1735,14 +1735,14 @@
> ##
> # @DirtyRateStatus:
> #
> -# An enumeration of dirtyrate status.
> +# Dirty page rate measurement status.
> #
> -# @unstarted: the dirtyrate thread has not been started.
> +# @unstarted: measuring thread has not been started yet
> #
> -# @measuring: the dirtyrate thread is measuring.
> +# @measuring: measuring thread is running
> #
> -# @measured: the dirtyrate thread has measured and results are
> -# available.
> +# @measured: dirty page rate is measured and the results are
> +# available
> #
> # Since: 5.2
> ##
> @@ -1752,13 +1752,14 @@
> ##
> # @DirtyRateMeasureMode:
> #
> -# An enumeration of mode of measuring dirtyrate.
> +# Method used to measure dirty page rate. Differences between
> +# available methods are explained in @calc-dirty-rate.
> #
> -# @page-sampling: calculate dirtyrate by sampling pages.
> +# @page-sampling: use page sampling
> #
> -# @dirty-ring: calculate dirtyrate by dirty ring.
> +# @dirty-ring: use dirty ring
> #
> -# @dirty-bitmap: calculate dirtyrate by dirty bitmap.
> +# @dirty-bitmap: use dirty bitmap
> #
> # Since: 6.2
> ##
> @@ -1768,26 +1769,25 @@
> ##
> # @DirtyRateInfo:
> #
> -# Information about current dirty page rate of vm.
> +# Information about measured dirty page rate.
> #
> # @dirty-rate: an estimate of the dirty page rate of the VM in units
> -# of MB/s, present only when estimating the rate has completed.
> +# of MiB/s. Value is present only when @status is 'measured'.
For consistency, please put two spaces between setences.
> #
> -# @status: status containing dirtyrate query status includes
> -# 'unstarted' or 'measuring' or 'measured'
> +# @status: current status of dirty page rate measurements
> #
> # @start-time: start time in units of second for calculation
> #
> -# @calc-time: time in units of second for sample dirty pages
> +# @calc-time: time period in units of second for which dirty page
> +# rate was measured
Maybe
# @calc-time: time period for which dirty page rate was measured
# (in seconds)
> #
> -# @sample-pages: page count per GB for sample dirty pages the default
> -# value is 512 (since 6.1)
> +# @sample-pages: number of sampled pages per each GiB of guest
per GiB
> +# memory. Value is valid only in page-sampling mode (Since 6.1)
Suggest "Valid only in ..."
> #
> -# @mode: mode containing method of calculate dirtyrate includes
> -# 'page-sampling' and 'dirty-ring' (Since 6.2)
> +# @mode: mode that was used to measure dirty page rate (Since 6.2)
> #
> -# @vcpu-dirty-rate: dirtyrate for each vcpu if dirty-ring mode
> -# specified (Since 6.2)
> +# @vcpu-dirty-rate: dirty rate for each vCPU if dirty-ring mode
> +# was specified (Since 6.2)
> #
> # Since: 5.2
> ##
> @@ -1803,15 +1803,50 @@
> ##
> # @calc-dirty-rate:
> #
> -# start calculating dirty page rate for vm
> -#
> -# @calc-time: time in units of second for sample dirty pages
> -#
> -# @sample-pages: page count per GB for sample dirty pages the default
> -# value is 512 (since 6.1)
> -#
> -# @mode: mechanism of calculating dirtyrate includes 'page-sampling'
> -# and 'dirty-ring' (Since 6.1)
> +# Starts measuring dirty page rate of the VM. Results can be
Imperative mood: "Start measuring ..."
> +# retrieved with @query-dirty-rate after measurements are completed.
> +#
> +# Dirty page rate is the number of pages changed in a given time
> +# period expressed in MiB/s. The following methods of calculation
> +# are available:
> +#
> +# 1. In page sampling mode, a random subset of pages are selected
> +# and hashed twice: once in the beginning of measurement time
Suggest "once at the beginning"
> +# period, another one -- in the end. If two hashes for some page
Suggest ", and once again at the end".
> +# are different, the page is counted as changed. Since this
> +# method relies on sampling and hashing, calculated dirty page
> +# rate is only the estimation of its true value. Setting
> +# @sample-pages to higher value improves estimation quality but
Suggest "Increasing @sample-pages improves estimation quality at the
cost ..."
> +# at the cost of higher computational overhead.
> +#
> +# 2. Dirty bitmap mode captures writes to memory by temporarily
> +# revoking write access to all pages and counting page faults.
Comma before "and".
> +# Information about modified pages is collected into bitmap,
"into a bitmap"
> +# where each bit corresponds to one guest page. This mode
> +# requires that KVM accelerator property "dirty-ring-size=N"
Suggest just "dirty-ring-size" (omit "=N").
> +# is *not* set.
> +#
> +# 3. Dirty ring mode is similar to dirty bitmap mode, but the
> +# information about modified pages is collected into ring buffer.
> +# This mode tracks page modification per each vCPU separately.
Either "for each vCPU" or "per vCPU".
> +# It requires that KVM accelerator property "dirty-ring-size=N"
> +# is set.
Suggest just "dirty-ring-size" (omit "=N").
> +#
> +# @calc-time: time period in units of second for which dirty page rate
> +# is calculated. Note that larger @calc-time values will typically
> +# result in smaller dirty page rates because page dirtying is a
> +# one-time event. Once some page is counted as dirty during
> +# @calc-time period, further writes to this page will not increase
> +# dirty page rate anymore.
Please indent one more, for consistency.
> +#
> +# @sample-pages: number of sampled pages per each GiB of guest memory.
> +# Default value is 512. For 4KiB guest pages this corresponds to
> +# sampling ratio of 0.2%. This argument is used only in page
> +# sampling mode. (Since 6.1)
Two spaces between '.' and '(', please.
> +#
> +# @mode: mechanism for tracking dirty pages. Default value is
> +# 'page-sampling'. Others are 'dirty-bitmap' and 'dirty-ring'.
> +# (Since 6.1)
> #
> # Since: 5.2
> #
> @@ -1828,9 +1863,21 @@
> ##
> # @query-dirty-rate:
> #
> -# query dirty page rate in units of MB/s for vm
> +# Query results of the most recent invocation of @calc-dirty-rate.
> #
> # Since: 5.2
> +#
> +# Examples:
> +#
> +# 1. Measurement is in progress:
> +#
> +# <- {"status": "measuring", "sample-pages": 512,
> +# "mode": "page-sampling", "start-time": 3665220, "calc-time": 10}
> +#
> +# 2. Measurement has been completed:
> +#
> +# <- {"status": "measured", "sample-pages": 512, "dirty-rate": 108,
> +# "mode": "page-sampling", "start-time": 3665220, "calc-time": 10}
> ##
> { 'command': 'query-dirty-rate', 'returns': 'DirtyRateInfo' }
This is *sooo* much better than before. Thank you!
An R-by from a migration maintainer would be nice.
If you agree with my suggestions, I can apply them in my tree, saving
you a respin. Let me know.
Acked-by: Markus Armbruster <armbru@redhat.com>
On Thu, May 25, 2023 at 03:08:35PM +0200, Markus Armbruster wrote:
> Andrei Gudkov <gudkov.andrei@huawei.com> writes:
>
> > Rewrote calc-dirty-rate documentation. Briefly described
> > different modes of dirty page rate measurement. Added some
> > examples. Fixed obvious grammar errors.
> >
> > Signed-off-by: Andrei Gudkov <gudkov.andrei@huawei.com>
> > ---
> > qapi/migration.json | 107 +++++++++++++++++++++++++++++++-------------
> > 1 file changed, 77 insertions(+), 30 deletions(-)
> >
> > diff --git a/qapi/migration.json b/qapi/migration.json
> > index 179af0c4d8..19b51444b5 100644
> > --- a/qapi/migration.json
> > +++ b/qapi/migration.json
> > @@ -1735,14 +1735,14 @@
> > ##
> > # @DirtyRateStatus:
> > #
> > -# An enumeration of dirtyrate status.
> > +# Dirty page rate measurement status.
> > #
> > -# @unstarted: the dirtyrate thread has not been started.
> > +# @unstarted: measuring thread has not been started yet
> > #
> > -# @measuring: the dirtyrate thread is measuring.
> > +# @measuring: measuring thread is running
> > #
> > -# @measured: the dirtyrate thread has measured and results are
> > -# available.
> > +# @measured: dirty page rate is measured and the results are
> > +# available
> > #
> > # Since: 5.2
> > ##
> > @@ -1752,13 +1752,14 @@
> > ##
> > # @DirtyRateMeasureMode:
> > #
> > -# An enumeration of mode of measuring dirtyrate.
> > +# Method used to measure dirty page rate. Differences between
> > +# available methods are explained in @calc-dirty-rate.
> > #
> > -# @page-sampling: calculate dirtyrate by sampling pages.
> > +# @page-sampling: use page sampling
> > #
> > -# @dirty-ring: calculate dirtyrate by dirty ring.
> > +# @dirty-ring: use dirty ring
> > #
> > -# @dirty-bitmap: calculate dirtyrate by dirty bitmap.
> > +# @dirty-bitmap: use dirty bitmap
> > #
> > # Since: 6.2
> > ##
> > @@ -1768,26 +1769,25 @@
> > ##
> > # @DirtyRateInfo:
> > #
> > -# Information about current dirty page rate of vm.
> > +# Information about measured dirty page rate.
> > #
> > # @dirty-rate: an estimate of the dirty page rate of the VM in units
> > -# of MB/s, present only when estimating the rate has completed.
> > +# of MiB/s. Value is present only when @status is 'measured'.
>
> For consistency, please put two spaces between setences.
>
> > #
> > -# @status: status containing dirtyrate query status includes
> > -# 'unstarted' or 'measuring' or 'measured'
> > +# @status: current status of dirty page rate measurements
> > #
> > # @start-time: start time in units of second for calculation
> > #
> > -# @calc-time: time in units of second for sample dirty pages
> > +# @calc-time: time period in units of second for which dirty page
> > +# rate was measured
>
> Maybe
>
> # @calc-time: time period for which dirty page rate was measured
> # (in seconds)
>
> > #
> > -# @sample-pages: page count per GB for sample dirty pages the default
> > -# value is 512 (since 6.1)
> > +# @sample-pages: number of sampled pages per each GiB of guest
>
> per GiB
>
> > +# memory. Value is valid only in page-sampling mode (Since 6.1)
>
> Suggest "Valid only in ..."
>
> > #
> > -# @mode: mode containing method of calculate dirtyrate includes
> > -# 'page-sampling' and 'dirty-ring' (Since 6.2)
> > +# @mode: mode that was used to measure dirty page rate (Since 6.2)
> > #
> > -# @vcpu-dirty-rate: dirtyrate for each vcpu if dirty-ring mode
> > -# specified (Since 6.2)
> > +# @vcpu-dirty-rate: dirty rate for each vCPU if dirty-ring mode
> > +# was specified (Since 6.2)
> > #
> > # Since: 5.2
> > ##
> > @@ -1803,15 +1803,50 @@
> > ##
> > # @calc-dirty-rate:
> > #
> > -# start calculating dirty page rate for vm
> > -#
> > -# @calc-time: time in units of second for sample dirty pages
> > -#
> > -# @sample-pages: page count per GB for sample dirty pages the default
> > -# value is 512 (since 6.1)
> > -#
> > -# @mode: mechanism of calculating dirtyrate includes 'page-sampling'
> > -# and 'dirty-ring' (Since 6.1)
> > +# Starts measuring dirty page rate of the VM. Results can be
>
> Imperative mood: "Start measuring ..."
>
> > +# retrieved with @query-dirty-rate after measurements are completed.
> > +#
> > +# Dirty page rate is the number of pages changed in a given time
> > +# period expressed in MiB/s. The following methods of calculation
> > +# are available:
> > +#
> > +# 1. In page sampling mode, a random subset of pages are selected
> > +# and hashed twice: once in the beginning of measurement time
>
> Suggest "once at the beginning"
>
> > +# period, another one -- in the end. If two hashes for some page
>
> Suggest ", and once again at the end".
>
> > +# are different, the page is counted as changed. Since this
> > +# method relies on sampling and hashing, calculated dirty page
> > +# rate is only the estimation of its true value. Setting
> > +# @sample-pages to higher value improves estimation quality but
>
> Suggest "Increasing @sample-pages improves estimation quality at the
> cost ..."
>
> > +# at the cost of higher computational overhead.
> > +#
> > +# 2. Dirty bitmap mode captures writes to memory by temporarily
> > +# revoking write access to all pages and counting page faults.
>
> Comma before "and".
>
> > +# Information about modified pages is collected into bitmap,
>
> "into a bitmap"
>
> > +# where each bit corresponds to one guest page. This mode
> > +# requires that KVM accelerator property "dirty-ring-size=N"
>
> Suggest just "dirty-ring-size" (omit "=N").
>
> > +# is *not* set.
> > +#
> > +# 3. Dirty ring mode is similar to dirty bitmap mode, but the
> > +# information about modified pages is collected into ring buffer.
> > +# This mode tracks page modification per each vCPU separately.
>
> Either "for each vCPU" or "per vCPU".
>
> > +# It requires that KVM accelerator property "dirty-ring-size=N"
> > +# is set.
>
> Suggest just "dirty-ring-size" (omit "=N").
>
> > +#
> > +# @calc-time: time period in units of second for which dirty page rate
> > +# is calculated. Note that larger @calc-time values will typically
> > +# result in smaller dirty page rates because page dirtying is a
> > +# one-time event. Once some page is counted as dirty during
> > +# @calc-time period, further writes to this page will not increase
> > +# dirty page rate anymore.
>
> Please indent one more, for consistency.
>
> > +#
> > +# @sample-pages: number of sampled pages per each GiB of guest memory.
> > +# Default value is 512. For 4KiB guest pages this corresponds to
> > +# sampling ratio of 0.2%. This argument is used only in page
> > +# sampling mode. (Since 6.1)
>
> Two spaces between '.' and '(', please.
>
> > +#
> > +# @mode: mechanism for tracking dirty pages. Default value is
> > +# 'page-sampling'. Others are 'dirty-bitmap' and 'dirty-ring'.
> > +# (Since 6.1)
> > #
> > # Since: 5.2
> > #
> > @@ -1828,9 +1863,21 @@
> > ##
> > # @query-dirty-rate:
> > #
> > -# query dirty page rate in units of MB/s for vm
> > +# Query results of the most recent invocation of @calc-dirty-rate.
> > #
> > # Since: 5.2
> > +#
> > +# Examples:
> > +#
> > +# 1. Measurement is in progress:
> > +#
> > +# <- {"status": "measuring", "sample-pages": 512,
> > +# "mode": "page-sampling", "start-time": 3665220, "calc-time": 10}
> > +#
> > +# 2. Measurement has been completed:
> > +#
> > +# <- {"status": "measured", "sample-pages": 512, "dirty-rate": 108,
> > +# "mode": "page-sampling", "start-time": 3665220, "calc-time": 10}
> > ##
> > { 'command': 'query-dirty-rate', 'returns': 'DirtyRateInfo' }
>
> This is *sooo* much better than before. Thank you!
>
> An R-by from a migration maintainer would be nice.
>
> If you agree with my suggestions, I can apply them in my tree, saving
> you a respin. Let me know.
Yes, sure. Please include also suggestion about wr-protect from Peter. Thanks.
>
> Acked-by: Markus Armbruster <armbru@redhat.com>
<gudkov.andrei@huawei.com> writes: > On Thu, May 25, 2023 at 03:08:35PM +0200, Markus Armbruster wrote: >> Andrei Gudkov <gudkov.andrei@huawei.com> writes: >> >> > Rewrote calc-dirty-rate documentation. Briefly described >> > different modes of dirty page rate measurement. Added some >> > examples. Fixed obvious grammar errors. >> > >> > Signed-off-by: Andrei Gudkov <gudkov.andrei@huawei.com> >> > --- >> > qapi/migration.json | 107 +++++++++++++++++++++++++++++++------------- >> > 1 file changed, 77 insertions(+), 30 deletions(-) >> > >> > diff --git a/qapi/migration.json b/qapi/migration.json >> > index 179af0c4d8..19b51444b5 100644 >> > --- a/qapi/migration.json >> > +++ b/qapi/migration.json [...] >> > -# @sample-pages: page count per GB for sample dirty pages the default >> > -# value is 512 (since 6.1) >> > +# @sample-pages: number of sampled pages per each GiB of guest >> >> per GiB >> >> > +# memory. Value is valid only in page-sampling mode (Since 6.1) >> >> Suggest "Valid only in ..." Outside this patch's scope, but here goes anway: I think we should have made this member optional, and present only when it's actually valid. Too late. [...] >> > +# Dirty page rate is the number of pages changed in a given time >> > +# period expressed in MiB/s. The following methods of calculation >> > +# are available: >> > +# >> > +# 1. In page sampling mode, a random subset of pages are selected >> > +# and hashed twice: once in the beginning of measurement time >> >> Suggest "once at the beginning" >> >> > +# period, another one -- in the end. If two hashes for some page >> >> Suggest ", and once again at the end". >> >> > +# are different, the page is counted as changed. Since this >> > +# method relies on sampling and hashing, calculated dirty page >> > +# rate is only the estimation of its true value. Setting I'll change this to "is only an estimate of" if you don't mind. [...] >> This is *sooo* much better than before. Thank you! >> >> An R-by from a migration maintainer would be nice. Got Peter's Acked-by now; all set. >> If you agree with my suggestions, I can apply them in my tree, saving >> you a respin. Let me know. > > Yes, sure. Please include also suggestion about wr-protect from Peter. Thanks. Done. >> Acked-by: Markus Armbruster <armbru@redhat.com> Queued. Thanks!
On Thu, May 25, 2023 at 03:08:35PM +0200, Markus Armbruster wrote:
> Andrei Gudkov <gudkov.andrei@huawei.com> writes:
>
> > Rewrote calc-dirty-rate documentation. Briefly described
> > different modes of dirty page rate measurement. Added some
> > examples. Fixed obvious grammar errors.
> >
> > Signed-off-by: Andrei Gudkov <gudkov.andrei@huawei.com>
> > ---
> > qapi/migration.json | 107 +++++++++++++++++++++++++++++++-------------
> > 1 file changed, 77 insertions(+), 30 deletions(-)
> >
> > diff --git a/qapi/migration.json b/qapi/migration.json
> > index 179af0c4d8..19b51444b5 100644
> > --- a/qapi/migration.json
> > +++ b/qapi/migration.json
> > @@ -1735,14 +1735,14 @@
> > ##
> > # @DirtyRateStatus:
> > #
> > -# An enumeration of dirtyrate status.
> > +# Dirty page rate measurement status.
> > #
> > -# @unstarted: the dirtyrate thread has not been started.
> > +# @unstarted: measuring thread has not been started yet
> > #
> > -# @measuring: the dirtyrate thread is measuring.
> > +# @measuring: measuring thread is running
> > #
> > -# @measured: the dirtyrate thread has measured and results are
> > -# available.
> > +# @measured: dirty page rate is measured and the results are
> > +# available
> > #
> > # Since: 5.2
> > ##
> > @@ -1752,13 +1752,14 @@
> > ##
> > # @DirtyRateMeasureMode:
> > #
> > -# An enumeration of mode of measuring dirtyrate.
> > +# Method used to measure dirty page rate. Differences between
> > +# available methods are explained in @calc-dirty-rate.
> > #
> > -# @page-sampling: calculate dirtyrate by sampling pages.
> > +# @page-sampling: use page sampling
> > #
> > -# @dirty-ring: calculate dirtyrate by dirty ring.
> > +# @dirty-ring: use dirty ring
> > #
> > -# @dirty-bitmap: calculate dirtyrate by dirty bitmap.
> > +# @dirty-bitmap: use dirty bitmap
> > #
> > # Since: 6.2
> > ##
> > @@ -1768,26 +1769,25 @@
> > ##
> > # @DirtyRateInfo:
> > #
> > -# Information about current dirty page rate of vm.
> > +# Information about measured dirty page rate.
> > #
> > # @dirty-rate: an estimate of the dirty page rate of the VM in units
> > -# of MB/s, present only when estimating the rate has completed.
> > +# of MiB/s. Value is present only when @status is 'measured'.
>
> For consistency, please put two spaces between setences.
>
> > #
> > -# @status: status containing dirtyrate query status includes
> > -# 'unstarted' or 'measuring' or 'measured'
> > +# @status: current status of dirty page rate measurements
> > #
> > # @start-time: start time in units of second for calculation
> > #
> > -# @calc-time: time in units of second for sample dirty pages
> > +# @calc-time: time period in units of second for which dirty page
> > +# rate was measured
>
> Maybe
>
> # @calc-time: time period for which dirty page rate was measured
> # (in seconds)
>
> > #
> > -# @sample-pages: page count per GB for sample dirty pages the default
> > -# value is 512 (since 6.1)
> > +# @sample-pages: number of sampled pages per each GiB of guest
>
> per GiB
>
> > +# memory. Value is valid only in page-sampling mode (Since 6.1)
>
> Suggest "Valid only in ..."
>
> > #
> > -# @mode: mode containing method of calculate dirtyrate includes
> > -# 'page-sampling' and 'dirty-ring' (Since 6.2)
> > +# @mode: mode that was used to measure dirty page rate (Since 6.2)
> > #
> > -# @vcpu-dirty-rate: dirtyrate for each vcpu if dirty-ring mode
> > -# specified (Since 6.2)
> > +# @vcpu-dirty-rate: dirty rate for each vCPU if dirty-ring mode
> > +# was specified (Since 6.2)
> > #
> > # Since: 5.2
> > ##
> > @@ -1803,15 +1803,50 @@
> > ##
> > # @calc-dirty-rate:
> > #
> > -# start calculating dirty page rate for vm
> > -#
> > -# @calc-time: time in units of second for sample dirty pages
> > -#
> > -# @sample-pages: page count per GB for sample dirty pages the default
> > -# value is 512 (since 6.1)
> > -#
> > -# @mode: mechanism of calculating dirtyrate includes 'page-sampling'
> > -# and 'dirty-ring' (Since 6.1)
> > +# Starts measuring dirty page rate of the VM. Results can be
>
> Imperative mood: "Start measuring ..."
>
> > +# retrieved with @query-dirty-rate after measurements are completed.
> > +#
> > +# Dirty page rate is the number of pages changed in a given time
> > +# period expressed in MiB/s. The following methods of calculation
> > +# are available:
> > +#
> > +# 1. In page sampling mode, a random subset of pages are selected
> > +# and hashed twice: once in the beginning of measurement time
>
> Suggest "once at the beginning"
>
> > +# period, another one -- in the end. If two hashes for some page
>
> Suggest ", and once again at the end".
>
> > +# are different, the page is counted as changed. Since this
> > +# method relies on sampling and hashing, calculated dirty page
> > +# rate is only the estimation of its true value. Setting
> > +# @sample-pages to higher value improves estimation quality but
>
> Suggest "Increasing @sample-pages improves estimation quality at the
> cost ..."
>
> > +# at the cost of higher computational overhead.
> > +#
> > +# 2. Dirty bitmap mode captures writes to memory by temporarily
> > +# revoking write access to all pages and counting page faults.
Just to mention that wr-protection is only one way to do this, IIUC that
depends on both arch (e.g. s390 impl KVM_GET_DIRTY_LOG totally differently
from x86) and also hardware capabilities (e.g. even on x86, PML enabled
hosts use dirty bits and PML-full vm exits rather than page faults).
But I think wr-protect may still be a good detailed showcase of it so
keeping it there looks very nice, perhaps just add "... writes to memory,
for example, by temporarily revoking ..."?
>
> Comma before "and".
>
> > +# Information about modified pages is collected into bitmap,
>
> "into a bitmap"
>
> > +# where each bit corresponds to one guest page. This mode
> > +# requires that KVM accelerator property "dirty-ring-size=N"
>
> Suggest just "dirty-ring-size" (omit "=N").
>
> > +# is *not* set.
> > +#
> > +# 3. Dirty ring mode is similar to dirty bitmap mode, but the
> > +# information about modified pages is collected into ring buffer.
> > +# This mode tracks page modification per each vCPU separately.
>
> Either "for each vCPU" or "per vCPU".
>
> > +# It requires that KVM accelerator property "dirty-ring-size=N"
> > +# is set.
>
> Suggest just "dirty-ring-size" (omit "=N").
>
> > +#
> > +# @calc-time: time period in units of second for which dirty page rate
> > +# is calculated. Note that larger @calc-time values will typically
> > +# result in smaller dirty page rates because page dirtying is a
> > +# one-time event. Once some page is counted as dirty during
> > +# @calc-time period, further writes to this page will not increase
> > +# dirty page rate anymore.
>
> Please indent one more, for consistency.
>
> > +#
> > +# @sample-pages: number of sampled pages per each GiB of guest memory.
> > +# Default value is 512. For 4KiB guest pages this corresponds to
> > +# sampling ratio of 0.2%. This argument is used only in page
> > +# sampling mode. (Since 6.1)
>
> Two spaces between '.' and '(', please.
>
> > +#
> > +# @mode: mechanism for tracking dirty pages. Default value is
> > +# 'page-sampling'. Others are 'dirty-bitmap' and 'dirty-ring'.
> > +# (Since 6.1)
> > #
> > # Since: 5.2
> > #
> > @@ -1828,9 +1863,21 @@
> > ##
> > # @query-dirty-rate:
> > #
> > -# query dirty page rate in units of MB/s for vm
> > +# Query results of the most recent invocation of @calc-dirty-rate.
> > #
> > # Since: 5.2
> > +#
> > +# Examples:
> > +#
> > +# 1. Measurement is in progress:
> > +#
> > +# <- {"status": "measuring", "sample-pages": 512,
> > +# "mode": "page-sampling", "start-time": 3665220, "calc-time": 10}
> > +#
> > +# 2. Measurement has been completed:
> > +#
> > +# <- {"status": "measured", "sample-pages": 512, "dirty-rate": 108,
> > +# "mode": "page-sampling", "start-time": 3665220, "calc-time": 10}
> > ##
> > { 'command': 'query-dirty-rate', 'returns': 'DirtyRateInfo' }
>
> This is *sooo* much better than before. Thank you!
I also agree. :)
>
> An R-by from a migration maintainer would be nice.
Only one migration maintainer now, but we have two reviewers.
Here's one from the reviewers' list:
Acked-by: Peter Xu <peterx@redhat.com>
>
> If you agree with my suggestions, I can apply them in my tree, saving
> you a respin. Let me know.
>
> Acked-by: Markus Armbruster <armbru@redhat.com>
>
--
Peter Xu
Peter Xu <peterx@redhat.com> writes:
> On Thu, May 25, 2023 at 03:08:35PM +0200, Markus Armbruster wrote:
>> Andrei Gudkov <gudkov.andrei@huawei.com> writes:
>>
>> > Rewrote calc-dirty-rate documentation. Briefly described
>> > different modes of dirty page rate measurement. Added some
>> > examples. Fixed obvious grammar errors.
>> >
>> > Signed-off-by: Andrei Gudkov <gudkov.andrei@huawei.com>
>> > ---
>> > qapi/migration.json | 107 +++++++++++++++++++++++++++++++-------------
>> > 1 file changed, 77 insertions(+), 30 deletions(-)
>> >
>> > diff --git a/qapi/migration.json b/qapi/migration.json
>> > index 179af0c4d8..19b51444b5 100644
>> > --- a/qapi/migration.json
>> > +++ b/qapi/migration.json
[...]
>> > +# Dirty page rate is the number of pages changed in a given time
>> > +# period expressed in MiB/s. The following methods of calculation
>> > +# are available:
>> > +#
>> > +# 1. In page sampling mode, a random subset of pages are selected
>> > +# and hashed twice: once in the beginning of measurement time
>>
>> Suggest "once at the beginning"
>>
>> > +# period, another one -- in the end. If two hashes for some page
>>
>> Suggest ", and once again at the end".
>>
>> > +# are different, the page is counted as changed. Since this
>> > +# method relies on sampling and hashing, calculated dirty page
>> > +# rate is only the estimation of its true value. Setting
>> > +# @sample-pages to higher value improves estimation quality but
>>
>> Suggest "Increasing @sample-pages improves estimation quality at the
>> cost ..."
>>
>> > +# at the cost of higher computational overhead.
>> > +#
>> > +# 2. Dirty bitmap mode captures writes to memory by temporarily
>> > +# revoking write access to all pages and counting page faults.
>
> Just to mention that wr-protection is only one way to do this, IIUC that
> depends on both arch (e.g. s390 impl KVM_GET_DIRTY_LOG totally differently
> from x86) and also hardware capabilities (e.g. even on x86, PML enabled
> hosts use dirty bits and PML-full vm exits rather than page faults).
Good point.
> But I think wr-protect may still be a good detailed showcase of it so
> keeping it there looks very nice, perhaps just add "... writes to memory,
> for example, by temporarily revoking ..."?
Going with
# 2. Dirty bitmap mode captures writes to memory (for example by
# temporarily revoking write access to all pages) and counting page
# faults. Information about modified pages is collected into a
# bitmap, where each bit corresponds to one guest page. This mode
# requires that KVM accelerator property "dirty-ring-size" is *not*
# set.
if you don't mind.
[...]
>> This is *sooo* much better than before. Thank you!
>
> I also agree. :)
>
>>
>> An R-by from a migration maintainer would be nice.
>
> Only one migration maintainer now, but we have two reviewers.
>
> Here's one from the reviewers' list:
>
> Acked-by: Peter Xu <peterx@redhat.com>
Thanks!
[...]
On Fri, May 26, 2023 at 01:23:07PM +0200, Markus Armbruster wrote: > Going with > > # 2. Dirty bitmap mode captures writes to memory (for example by > # temporarily revoking write access to all pages) and counting page > # faults. Information about modified pages is collected into a > # bitmap, where each bit corresponds to one guest page. This mode > # requires that KVM accelerator property "dirty-ring-size" is *not* > # set. > > if you don't mind. Looks good here, thanks! -- Peter Xu
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