mbm_bw_count() is only called by the mbm_handle_overflow() worker once a
second. It reads the hardware register, calculates the bandwidth and
updates m->prev_bw_msr which is used to hold the previous hardware register
value.
Operating directly on hardware register values makes it difficult to make
this code architecture independent, so that it can be moved to /fs/,
making the mba_sc feature something resctrl supports with no additional
support from the architecture.
Prior to calling mbm_bw_count(), mbm_update() reads from the same hardware
register using __mon_event_count().
Change mbm_bw_count() to use the current chunks value most recently saved
by __mon_event_count(). This removes an extra call to __rmid_read().
Instead of using m->prev_msr to calculate the number of chunks seen,
use the rr->val that was updated by __mon_event_count(). This removes an
extra call to mbm_overflow_count() and get_corrected_mbm_count().
Calculating bandwidth like this means mbm_bw_count() no longer operates
on hardware register values directly.
Reviewed-by: Jamie Iles <quic_jiles@quicinc.com>
Tested-by: Xin Hao <xhao@linux.alibaba.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-by: Cristian Marussi <cristian.marussi@arm.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since v3:
* Reset rr.val before each use to avoid over counting.
* Fixed typos in kerneldoc.
Changes since v2:
* Expanded commit message
Changes since v1:
* This patch was rewritten
---
arch/x86/kernel/cpu/resctrl/internal.h | 4 ++--
arch/x86/kernel/cpu/resctrl/monitor.c | 25 ++++++++++++++++---------
2 files changed, 18 insertions(+), 11 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 3b9e43ba7590..46062099d69e 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -289,7 +289,7 @@ struct rftype {
* struct mbm_state - status for each MBM counter in each domain
* @chunks: Total data moved (multiply by rdt_group.mon_scale to get bytes)
* @prev_msr: Value of IA32_QM_CTR for this RMID last time we read it
- * @prev_bw_msr:Value of previous IA32_QM_CTR for bandwidth counting
+ * @prev_bw_chunks: Previous chunks value read for bandwidth calculation
* @prev_bw: The most recent bandwidth in MBps
* @delta_bw: Difference between the current and previous bandwidth
* @delta_comp: Indicates whether to compute the delta_bw
@@ -297,7 +297,7 @@ struct rftype {
struct mbm_state {
u64 chunks;
u64 prev_msr;
- u64 prev_bw_msr;
+ u64 prev_bw_chunks;
u32 prev_bw;
u32 delta_bw;
bool delta_comp;
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 3e69386cfe00..2d81b6cd9632 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -315,7 +315,7 @@ static u64 __mon_event_count(u32 rmid, struct rmid_read *rr)
if (rr->first) {
memset(m, 0, sizeof(struct mbm_state));
- m->prev_bw_msr = m->prev_msr = tval;
+ m->prev_msr = tval;
return 0;
}
@@ -329,27 +329,32 @@ static u64 __mon_event_count(u32 rmid, struct rmid_read *rr)
}
/*
+ * mbm_bw_count() - Update bw count from values previously read by
+ * __mon_event_count().
+ * @rmid: The rmid used to identify the cached mbm_state.
+ * @rr: The struct rmid_read populated by __mon_event_count().
+ *
* Supporting function to calculate the memory bandwidth
- * and delta bandwidth in MBps.
+ * and delta bandwidth in MBps. The chunks value previously read by
+ * __mon_event_count() is compared with the chunks value from the previous
+ * invocation. This must be called once per second to maintain values in MBps.
*/
static void mbm_bw_count(u32 rmid, struct rmid_read *rr)
{
struct rdt_hw_resource *hw_res = resctrl_to_arch_res(rr->r);
struct mbm_state *m = &rr->d->mbm_local[rmid];
- u64 tval, cur_bw, chunks;
+ u64 cur_bw, chunks, cur_chunks;
- tval = __rmid_read(rmid, rr->evtid);
- if (tval & (RMID_VAL_ERROR | RMID_VAL_UNAVAIL))
- return;
+ cur_chunks = rr->val;
+ chunks = cur_chunks - m->prev_bw_chunks;
+ m->prev_bw_chunks = cur_chunks;
- chunks = mbm_overflow_count(m->prev_bw_msr, tval, hw_res->mbm_width);
- cur_bw = (get_corrected_mbm_count(rmid, chunks) * hw_res->mon_scale) >> 20;
+ cur_bw = (chunks * hw_res->mon_scale) >> 20;
if (m->delta_comp)
m->delta_bw = abs(cur_bw - m->prev_bw);
m->delta_comp = false;
m->prev_bw = cur_bw;
- m->prev_bw_msr = tval;
}
/*
@@ -516,10 +521,12 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d, int rmid)
*/
if (is_mbm_total_enabled()) {
rr.evtid = QOS_L3_MBM_TOTAL_EVENT_ID;
+ rr.val = 0;
__mon_event_count(rmid, &rr);
}
if (is_mbm_local_enabled()) {
rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
+ rr.val = 0;
__mon_event_count(rmid, &rr);
/*
--
2.30.2
在 2022/9/2 下午11:48, James Morse 写道:
> mbm_bw_count() is only called by the mbm_handle_overflow() worker once a
> second. It reads the hardware register, calculates the bandwidth and
> updates m->prev_bw_msr which is used to hold the previous hardware register
> value.
>
> Operating directly on hardware register values makes it difficult to make
> this code architecture independent, so that it can be moved to /fs/,
> making the mba_sc feature something resctrl supports with no additional
> support from the architecture.
> Prior to calling mbm_bw_count(), mbm_update() reads from the same hardware
> register using __mon_event_count().
>
> Change mbm_bw_count() to use the current chunks value most recently saved
> by __mon_event_count(). This removes an extra call to __rmid_read().
> Instead of using m->prev_msr to calculate the number of chunks seen,
> use the rr->val that was updated by __mon_event_count(). This removes an
> extra call to mbm_overflow_count() and get_corrected_mbm_count().
> Calculating bandwidth like this means mbm_bw_count() no longer operates
> on hardware register values directly.
>
> Reviewed-by: Jamie Iles <quic_jiles@quicinc.com>
> Tested-by: Xin Hao <xhao@linux.alibaba.com>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Tested-by: Cristian Marussi <cristian.marussi@arm.com>
> Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v3:
> * Reset rr.val before each use to avoid over counting.
> * Fixed typos in kerneldoc.
>
> Changes since v2:
> * Expanded commit message
>
> Changes since v1:
> * This patch was rewritten
> ---
> arch/x86/kernel/cpu/resctrl/internal.h | 4 ++--
> arch/x86/kernel/cpu/resctrl/monitor.c | 25 ++++++++++++++++---------
> 2 files changed, 18 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 3b9e43ba7590..46062099d69e 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -289,7 +289,7 @@ struct rftype {
> * struct mbm_state - status for each MBM counter in each domain
> * @chunks: Total data moved (multiply by rdt_group.mon_scale to get bytes)
> * @prev_msr: Value of IA32_QM_CTR for this RMID last time we read it
> - * @prev_bw_msr:Value of previous IA32_QM_CTR for bandwidth counting
> + * @prev_bw_chunks: Previous chunks value read for bandwidth calculation
> * @prev_bw: The most recent bandwidth in MBps
> * @delta_bw: Difference between the current and previous bandwidth
> * @delta_comp: Indicates whether to compute the delta_bw
> @@ -297,7 +297,7 @@ struct rftype {
> struct mbm_state {
> u64 chunks;
> u64 prev_msr;
> - u64 prev_bw_msr;
> + u64 prev_bw_chunks;
> u32 prev_bw;
> u32 delta_bw;
> bool delta_comp;
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 3e69386cfe00..2d81b6cd9632 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -315,7 +315,7 @@ static u64 __mon_event_count(u32 rmid, struct rmid_read *rr)
>
> if (rr->first) {
> memset(m, 0, sizeof(struct mbm_state));
> - m->prev_bw_msr = m->prev_msr = tval;
> + m->prev_msr = tval;
> return 0;
> }
>
> @@ -329,27 +329,32 @@ static u64 __mon_event_count(u32 rmid, struct rmid_read *rr)
> }
>
> /*
> + * mbm_bw_count() - Update bw count from values previously read by
> + * __mon_event_count().
> + * @rmid: The rmid used to identify the cached mbm_state.
> + * @rr: The struct rmid_read populated by __mon_event_count().
> + *
> * Supporting function to calculate the memory bandwidth
> - * and delta bandwidth in MBps.
> + * and delta bandwidth in MBps. The chunks value previously read by
> + * __mon_event_count() is compared with the chunks value from the previous
> + * invocation. This must be called once per second to maintain values in MBps.
> */
> static void mbm_bw_count(u32 rmid, struct rmid_read *rr)
> {
> struct rdt_hw_resource *hw_res = resctrl_to_arch_res(rr->r);
> struct mbm_state *m = &rr->d->mbm_local[rmid];
> - u64 tval, cur_bw, chunks;
> + u64 cur_bw, chunks, cur_chunks;
>
> - tval = __rmid_read(rmid, rr->evtid);
> - if (tval & (RMID_VAL_ERROR | RMID_VAL_UNAVAIL))
> - return;
> + cur_chunks = rr->val;
> + chunks = cur_chunks - m->prev_bw_chunks;
> + m->prev_bw_chunks = cur_chunks;
>
> - chunks = mbm_overflow_count(m->prev_bw_msr, tval, hw_res->mbm_width);
> - cur_bw = (get_corrected_mbm_count(rmid, chunks) * hw_res->mon_scale) >> 20;
> + cur_bw = (chunks * hw_res->mon_scale) >> 20;
>
> if (m->delta_comp)
> m->delta_bw = abs(cur_bw - m->prev_bw);
> m->delta_comp = false;
> m->prev_bw = cur_bw;
> - m->prev_bw_msr = tval;
> }
>
> /*
> @@ -516,10 +521,12 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d, int rmid)
> */
> if (is_mbm_total_enabled()) {
> rr.evtid = QOS_L3_MBM_TOTAL_EVENT_ID;
> + rr.val = 0;
In mbm_update, there no use the rr.val, so there no need to initialize ？
> __mon_event_count(rmid, &rr);
> }
> if (is_mbm_local_enabled()) {
> rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
> + rr.val = 0;
ditto.
> __mon_event_count(rmid, &rr);
>
> /*
Hi Hao Xin,
On 07/09/2022 07:47, haoxin wrote:
> 在 2022/9/2 下午11:48, James Morse 写道:
>> mbm_bw_count() is only called by the mbm_handle_overflow() worker once a
>> second. It reads the hardware register, calculates the bandwidth and
>> updates m->prev_bw_msr which is used to hold the previous hardware register
>> value.
>>
>> Operating directly on hardware register values makes it difficult to make
>> this code architecture independent, so that it can be moved to /fs/,
>> making the mba_sc feature something resctrl supports with no additional
>> support from the architecture.
>> Prior to calling mbm_bw_count(), mbm_update() reads from the same hardware
>> register using __mon_event_count().
>>
>> Change mbm_bw_count() to use the current chunks value most recently saved
>> by __mon_event_count(). This removes an extra call to __rmid_read().
>> Instead of using m->prev_msr to calculate the number of chunks seen,
>> use the rr->val that was updated by __mon_event_count(). This removes an
>> extra call to mbm_overflow_count() and get_corrected_mbm_count().
>> Calculating bandwidth like this means mbm_bw_count() no longer operates
>> on hardware register values directly.
>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index 3e69386cfe00..2d81b6cd9632 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -516,10 +521,12 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain
>> *d, int rmid)
>> */
>> if (is_mbm_total_enabled()) {
>> rr.evtid = QOS_L3_MBM_TOTAL_EVENT_ID;>> + rr.val = 0;
> In mbm_update, there no use the rr.val, so there no need to initialize ？
>> __mon_event_count(rmid, &rr);
>> }
>> if (is_mbm_local_enabled()) {
>> rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
>> + rr.val = 0;
> ditto.
>> __mon_event_count(rmid, &rr);
>> /*
No, but this just leaves that problem for someone else to discover the hard way! I think
its fair for the compiler to complain that addition on an uninitialised field is a bug.
I'd prefer to keep this as it is on the principle of 'least surprise'.
Thanks,
James
On 9/8/2022 10:00 AM, James Morse wrote:
> Hi Hao Xin,
>
> On 07/09/2022 07:47, haoxin wrote:
>> 在 2022/9/2 下午11:48, James Morse 写道:
>>> mbm_bw_count() is only called by the mbm_handle_overflow() worker once a
>>> second. It reads the hardware register, calculates the bandwidth and
>>> updates m->prev_bw_msr which is used to hold the previous hardware register
>>> value.
>>>
>>> Operating directly on hardware register values makes it difficult to make
>>> this code architecture independent, so that it can be moved to /fs/,
>>> making the mba_sc feature something resctrl supports with no additional
>>> support from the architecture.
>>> Prior to calling mbm_bw_count(), mbm_update() reads from the same hardware
>>> register using __mon_event_count().
>>>
>>> Change mbm_bw_count() to use the current chunks value most recently saved
>>> by __mon_event_count(). This removes an extra call to __rmid_read().
>>> Instead of using m->prev_msr to calculate the number of chunks seen,
>>> use the rr->val that was updated by __mon_event_count(). This removes an
>>> extra call to mbm_overflow_count() and get_corrected_mbm_count().
>>> Calculating bandwidth like this means mbm_bw_count() no longer operates
>>> on hardware register values directly.
>
>>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>>> index 3e69386cfe00..2d81b6cd9632 100644
>>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>
>>> @@ -516,10 +521,12 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain
>>> *d, int rmid)
>>> */
>>> if (is_mbm_total_enabled()) {
>>> rr.evtid = QOS_L3_MBM_TOTAL_EVENT_ID;>> + rr.val = 0;
>
>> In mbm_update, there no use the rr.val, so there no need to initialize ？
This patch introduces using rr.val into mbm_bw_count() that is called
from mbm_update(). This patch thus introduces the requirement that rr.val needs
to be initialized.
>
>>> __mon_event_count(rmid, &rr);
>>> }
>>> if (is_mbm_local_enabled()) {
>>> rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
>>> + rr.val = 0;
>
>> ditto.
>
>>> __mon_event_count(rmid, &rr);
>>> /*
>
> No, but this just leaves that problem for someone else to discover the hard way! I think
> its fair for the compiler to complain that addition on an uninitialised field is a bug.
>
> I'd prefer to keep this as it is on the principle of 'least surprise'.
Yes, please do keep this. If rr.val is not initialized then the software controller will
use wrong data to compute the delta bandwidth.
Reinette
The following commit has been merged into the x86/cache branch of tip:
Commit-ID: 30442571ec81fb33f7bd8cea5a14afb10b8f442a
Gitweb: https://git.kernel.org/tip/30442571ec81fb33f7bd8cea5a14afb10b8f442a
Author: James Morse <james.morse@arm.com>
AuthorDate: Fri, 02 Sep 2022 15:48:20
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Thu, 22 Sep 2022 17:44:57 +02:00
x86/resctrl: Calculate bandwidth from the previous __mon_event_count() chunks
mbm_bw_count() is only called by the mbm_handle_overflow() worker once a
second. It reads the hardware register, calculates the bandwidth and
updates m->prev_bw_msr which is used to hold the previous hardware register
value.
Operating directly on hardware register values makes it difficult to make
this code architecture independent, so that it can be moved to /fs/,
making the mba_sc feature something resctrl supports with no additional
support from the architecture.
Prior to calling mbm_bw_count(), mbm_update() reads from the same hardware
register using __mon_event_count().
Change mbm_bw_count() to use the current chunks value most recently saved
by __mon_event_count(). This removes an extra call to __rmid_read().
Instead of using m->prev_msr to calculate the number of chunks seen,
use the rr->val that was updated by __mon_event_count(). This removes an
extra call to mbm_overflow_count() and get_corrected_mbm_count().
Calculating bandwidth like this means mbm_bw_count() no longer operates
on hardware register values directly.
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Jamie Iles <quic_jiles@quicinc.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Tested-by: Xin Hao <xhao@linux.alibaba.com>
Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-by: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/20220902154829.30399-13-james.morse@arm.com
---
arch/x86/kernel/cpu/resctrl/internal.h | 4 ++--
arch/x86/kernel/cpu/resctrl/monitor.c | 25 ++++++++++++++++---------
2 files changed, 18 insertions(+), 11 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 3b9e43b..4606209 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -289,7 +289,7 @@ struct rftype {
* struct mbm_state - status for each MBM counter in each domain
* @chunks: Total data moved (multiply by rdt_group.mon_scale to get bytes)
* @prev_msr: Value of IA32_QM_CTR for this RMID last time we read it
- * @prev_bw_msr:Value of previous IA32_QM_CTR for bandwidth counting
+ * @prev_bw_chunks: Previous chunks value read for bandwidth calculation
* @prev_bw: The most recent bandwidth in MBps
* @delta_bw: Difference between the current and previous bandwidth
* @delta_comp: Indicates whether to compute the delta_bw
@@ -297,7 +297,7 @@ struct rftype {
struct mbm_state {
u64 chunks;
u64 prev_msr;
- u64 prev_bw_msr;
+ u64 prev_bw_chunks;
u32 prev_bw;
u32 delta_bw;
bool delta_comp;
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 3e69386..2d81b6c 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -315,7 +315,7 @@ static u64 __mon_event_count(u32 rmid, struct rmid_read *rr)
if (rr->first) {
memset(m, 0, sizeof(struct mbm_state));
- m->prev_bw_msr = m->prev_msr = tval;
+ m->prev_msr = tval;
return 0;
}
@@ -329,27 +329,32 @@ static u64 __mon_event_count(u32 rmid, struct rmid_read *rr)
}
/*
+ * mbm_bw_count() - Update bw count from values previously read by
+ * __mon_event_count().
+ * @rmid: The rmid used to identify the cached mbm_state.
+ * @rr: The struct rmid_read populated by __mon_event_count().
+ *
* Supporting function to calculate the memory bandwidth
- * and delta bandwidth in MBps.
+ * and delta bandwidth in MBps. The chunks value previously read by
+ * __mon_event_count() is compared with the chunks value from the previous
+ * invocation. This must be called once per second to maintain values in MBps.
*/
static void mbm_bw_count(u32 rmid, struct rmid_read *rr)
{
struct rdt_hw_resource *hw_res = resctrl_to_arch_res(rr->r);
struct mbm_state *m = &rr->d->mbm_local[rmid];
- u64 tval, cur_bw, chunks;
+ u64 cur_bw, chunks, cur_chunks;
- tval = __rmid_read(rmid, rr->evtid);
- if (tval & (RMID_VAL_ERROR | RMID_VAL_UNAVAIL))
- return;
+ cur_chunks = rr->val;
+ chunks = cur_chunks - m->prev_bw_chunks;
+ m->prev_bw_chunks = cur_chunks;
- chunks = mbm_overflow_count(m->prev_bw_msr, tval, hw_res->mbm_width);
- cur_bw = (get_corrected_mbm_count(rmid, chunks) * hw_res->mon_scale) >> 20;
+ cur_bw = (chunks * hw_res->mon_scale) >> 20;
if (m->delta_comp)
m->delta_bw = abs(cur_bw - m->prev_bw);
m->delta_comp = false;
m->prev_bw = cur_bw;
- m->prev_bw_msr = tval;
}
/*
@@ -516,10 +521,12 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d, int rmid)
*/
if (is_mbm_total_enabled()) {
rr.evtid = QOS_L3_MBM_TOTAL_EVENT_ID;
+ rr.val = 0;
__mon_event_count(rmid, &rr);
}
if (is_mbm_local_enabled()) {
rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
+ rr.val = 0;
__mon_event_count(rmid, &rr);
/*© 2016 - 2026 Red Hat, Inc.