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[PATCH v4 1/2] migration/ram: Reduce unnecessary rate limiting

Kunkun Jiang posted 2 patches 4 years, 10 months ago
Maintainers: Juan Quintela <quintela@redhat.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>
[PATCH v4 1/2] migration/ram: Reduce unnecessary rate limiting
Posted by Kunkun Jiang 4 years, 10 months ago 
When the host page is a huge page and something is sent in the
current iteration, migration_rate_limit() should be executed.
If not, it can be omitted.

Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
Reviewed-by: David Edmondson <david.edmondson@oracle.com>
---
 migration/ram.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/migration/ram.c b/migration/ram.c
index 72143da0ac..3eb5b0d7a7 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -2015,8 +2015,13 @@ static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss,
 
         pages += tmppages;
         pss->page++;
-        /* Allow rate limiting to happen in the middle of huge pages */
-        migration_rate_limit();
+        /*
+         * Allow rate limiting to happen in the middle of huge pages if
+         * something is sent in the current iteration.
+         */
+        if (pagesize_bits > 1 && tmppages > 0) {
+            migration_rate_limit();
+        }
     } while ((pss->page & (pagesize_bits - 1)) &&
              offset_in_ramblock(pss->block,
                                 ((ram_addr_t)pss->page) << TARGET_PAGE_BITS));
-- 
2.23.0
Re: [PATCH v4 1/2] migration/ram: Reduce unnecessary rate limiting
Posted by Peter Xu 4 years, 10 months ago 
On Tue, Mar 16, 2021 at 08:57:15PM +0800, Kunkun Jiang wrote:
> When the host page is a huge page and something is sent in the
> current iteration, migration_rate_limit() should be executed.
> If not, it can be omitted.
> 
> Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
> Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
> Reviewed-by: David Edmondson <david.edmondson@oracle.com>
> ---
>  migration/ram.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 72143da0ac..3eb5b0d7a7 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -2015,8 +2015,13 @@ static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss,
>  
>          pages += tmppages;
>          pss->page++;
> -        /* Allow rate limiting to happen in the middle of huge pages */
> -        migration_rate_limit();
> +        /*
> +         * Allow rate limiting to happen in the middle of huge pages if
> +         * something is sent in the current iteration.
> +         */
> +        if (pagesize_bits > 1 && tmppages > 0) {
> +            migration_rate_limit();
> +        }

Sorry I'm still not a fan of this - I'd even prefer calling that once more just
to make sure it won't be forgotten to be called..  Not to say it's merely a noop.

I'll leave this to Dave..  Maybe I'm too harsh! :)

-- 
Peter Xu
Re: [PATCH v4 1/2] migration/ram: Reduce unnecessary rate limiting
Posted by Kunkun Jiang 4 years, 10 months ago 
Hi  Peter,

On 2021/3/17 5:39, Peter Xu wrote:
> On Tue, Mar 16, 2021 at 08:57:15PM +0800, Kunkun Jiang wrote:
>> When the host page is a huge page and something is sent in the
>> current iteration, migration_rate_limit() should be executed.
>> If not, it can be omitted.
>>
>> Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
>> Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
>> Reviewed-by: David Edmondson <david.edmondson@oracle.com>
>> ---
>>   migration/ram.c | 9 +++++++--
>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/migration/ram.c b/migration/ram.c
>> index 72143da0ac..3eb5b0d7a7 100644
>> --- a/migration/ram.c
>> +++ b/migration/ram.c
>> @@ -2015,8 +2015,13 @@ static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss,
>>   
>>           pages += tmppages;
>>           pss->page++;
>> -        /* Allow rate limiting to happen in the middle of huge pages */
>> -        migration_rate_limit();
>> +        /*
>> +         * Allow rate limiting to happen in the middle of huge pages if
>> +         * something is sent in the current iteration.
>> +         */
>> +        if (pagesize_bits > 1 && tmppages > 0) {
>> +            migration_rate_limit();
>> +        }
> Sorry I'm still not a fan of this - I'd even prefer calling that once more just
> to make sure it won't be forgotten to be called..  Not to say it's merely a noop.
>
> I'll leave this to Dave..  Maybe I'm too harsh! :)
>
You are very serious and meticulous. I like your character very much.😉
This patch was used to reviewed by David. So, I want to know what
his opinion is.

@David
Hi David, what is your opinion on this patch?

Thanks,
Kunkun Jiang
Re: [PATCH v4 1/2] migration/ram: Reduce unnecessary rate limiting
Posted by David Edmondson 4 years, 10 months ago 
On Wednesday, 2021-03-17 at 09:37:11 +08, Kunkun Jiang wrote:

> Hi  Peter,
>
> On 2021/3/17 5:39, Peter Xu wrote:
>> On Tue, Mar 16, 2021 at 08:57:15PM +0800, Kunkun Jiang wrote:
>>> When the host page is a huge page and something is sent in the
>>> current iteration, migration_rate_limit() should be executed.
>>> If not, it can be omitted.
>>>
>>> Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
>>> Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
>>> Reviewed-by: David Edmondson <david.edmondson@oracle.com>
>>> ---
>>>   migration/ram.c | 9 +++++++--
>>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/migration/ram.c b/migration/ram.c
>>> index 72143da0ac..3eb5b0d7a7 100644
>>> --- a/migration/ram.c
>>> +++ b/migration/ram.c
>>> @@ -2015,8 +2015,13 @@ static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss,
>>>   
>>>           pages += tmppages;
>>>           pss->page++;
>>> -        /* Allow rate limiting to happen in the middle of huge pages */
>>> -        migration_rate_limit();
>>> +        /*
>>> +         * Allow rate limiting to happen in the middle of huge pages if
>>> +         * something is sent in the current iteration.
>>> +         */
>>> +        if (pagesize_bits > 1 && tmppages > 0) {
>>> +            migration_rate_limit();
>>> +        }
>> Sorry I'm still not a fan of this - I'd even prefer calling that once more just
>> to make sure it won't be forgotten to be called..  Not to say it's merely a noop.
>>
>> I'll leave this to Dave..  Maybe I'm too harsh! :)
>>
> You are very serious and meticulous. I like your character very much.😉
> This patch was used to reviewed by David. So, I want to know what
> his opinion is.
>
> @David
> Hi David, what is your opinion on this patch?

I suspect that this referred to David Gilbert rather than me :-)

> Thanks,
> Kunkun Jiang

dme.
-- 
Time is waiting to explain, why refuse?
Re: [PATCH v4 1/2] migration/ram: Reduce unnecessary rate limiting
Posted by Dr. David Alan Gilbert 4 years, 10 months ago 
* Kunkun Jiang (jiangkunkun@huawei.com) wrote:
> Hi  Peter,
> 
> On 2021/3/17 5:39, Peter Xu wrote:
> > On Tue, Mar 16, 2021 at 08:57:15PM +0800, Kunkun Jiang wrote:
> > > When the host page is a huge page and something is sent in the
> > > current iteration, migration_rate_limit() should be executed.
> > > If not, it can be omitted.
> > > 
> > > Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
> > > Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
> > > Reviewed-by: David Edmondson <david.edmondson@oracle.com>
> > > ---
> > >   migration/ram.c | 9 +++++++--
> > >   1 file changed, 7 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/migration/ram.c b/migration/ram.c
> > > index 72143da0ac..3eb5b0d7a7 100644
> > > --- a/migration/ram.c
> > > +++ b/migration/ram.c
> > > @@ -2015,8 +2015,13 @@ static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss,
> > >           pages += tmppages;
> > >           pss->page++;
> > > -        /* Allow rate limiting to happen in the middle of huge pages */
> > > -        migration_rate_limit();
> > > +        /*
> > > +         * Allow rate limiting to happen in the middle of huge pages if
> > > +         * something is sent in the current iteration.
> > > +         */
> > > +        if (pagesize_bits > 1 && tmppages > 0) {
> > > +            migration_rate_limit();
> > > +        }
> > Sorry I'm still not a fan of this - I'd even prefer calling that once more just
> > to make sure it won't be forgotten to be called..  Not to say it's merely a noop.
> > 
> > I'll leave this to Dave..  Maybe I'm too harsh! :)
> > 
> You are very serious and meticulous. I like your character very much.😉
> This patch was used to reviewed by David. So, I want to know what
> his opinion is.
> 
> @David
> Hi David, what is your opinion on this patch?

Yes, I think this is OK;
  a) The qemu_file_rate_limit in the loop in ram_save_iterate still
     gets called, so that covers the 'pagesize_bits > 1' part of the if
  b) As soon as we send any part of the hugepage the 'tmppages > 0'
     triggers and we get the check back again.

So I guess this mostly helps the case where we have big huge pages
which are mostly not-dirty, and we spend a lot of time in
ram_save_host_page searching for the target page to send.



Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> Thanks,
> Kunkun Jiang
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

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