CPU cfs bandwidth controller uses hrtimer. Currently there is no initial
value set. Hence all period timers would align at expiry.
This happens when there are multiple CPU cgroup's.
There is a performance gain that can be achieved here if the timers are
interleaved when the utilization of each CPU cgroup is low and total
utilization of all the CPU cgroup's is less than 50%. If the timers are
interleaved, then the unthrottled cgroup can run freely without many
context switches and can also benefit from SMT Folding. This effect will
be further amplified in SPLPAR environment.
This commit adds a random offset after initializing each hrtimer. This
would result in interleaving the timers at expiry, which helps in achieving
the said performance gain.
This was tested on powerpc platform with 8 core SMT=8. Socket power was
measured when the workload. Benchmarked the stress-ng with power
information. Throughput oriented benchmarks show significant gain up to
25% while power consumption increases up to 15%.
Workload: stress-ng --cpu=32 --cpu-ops=50000.
1CG - 1 cgroup is running.
2CG - 2 cgroups are running together.
Time taken to complete stress-ng in seconds and power is in watts.
each cgroup is throttled at 25% with 100ms as the period value.
6.2-rc6 | with patch
8 core 1CG power 2CG power | 1CG power 2 CG power
27.5 80.6 40 90 | 27.3 82 32.3 104
27.5 81 40.2 91 | 27.5 81 38.7 96
27.7 80 40.1 89 | 27.6 80 29.7 106
27.7 80.1 40.3 94 | 27.6 80 31.5 105
Latency might be affected by this change. That could happen if the CPU was
in a deep idle state which is possible if we interleave the timers. Used
schbench for measuring the latency. Each cgroup is throttled at 25% with
period value is set to 100ms. Numbers are when both the cgroups are
running simultaneously. Latency values don't degrade much. Some
improvement is seen in tail latencies.
6.2-rc6 with patch
Groups: 16
50.0th: 39.5 42.5
75.0th: 924.0 922.0
90.0th: 972.0 968.0
95.0th: 1005.5 994.0
99.0th: 4166.0 2287.0
99.5th: 7314.0 7448.0
99.9th: 15024.0 13600.0
Groups: 32
50.0th: 819.0 463.0
75.0th: 1596.0 918.0
90.0th: 5992.0 1281.5
95.0th: 13184.0 2765.0
99.0th: 21792.0 14240.0
99.5th: 25696.0 18920.0
99.9th: 33280.0 35776.0
Groups: 64
50.0th: 4806.0 3440.0
75.0th: 31136.0 33664.0
90.0th: 54144.0 58752.0
95.0th: 66176.0 67200.0
99.0th: 84736.0 91520.0
99.5th: 97408.0 114048.0
99.9th: 136448.0 140032.0
Signed-off-by: Shrikanth Hegde<[email protected]>
Suggested-by: Peter Zijlstra <[email protected]>
Suggested-by: Thomas Gleixner <[email protected]>
Initial RFC PATCH, discussions and details on the problem:
Link1: https://lore.kernel.org/lkml/[email protected]/
Link2: https://lore.kernel.org/lkml/[email protected]/
---
kernel/sched/fair.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ff4dbbae3b10..2a4a0969e04f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5923,6 +5923,10 @@ void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq);
hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED);
cfs_b->period_timer.function = sched_cfs_period_timer;
+
+ /* Add a random offset so that timers interleave */
+ hrtimer_set_expires(&cfs_b->period_timer,
+ get_random_u32_below(cfs_b->period));
hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
cfs_b->slack_timer.function = sched_cfs_slack_timer;
cfs_b->slack_started = false;
--
2.31.1
Shrikanth Hegde <[email protected]> writes:
> CPU cfs bandwidth controller uses hrtimer. Currently there is no initial
> value set. Hence all period timers would align at expiry.
> This happens when there are multiple CPU cgroup's.
>
> There is a performance gain that can be achieved here if the timers are
> interleaved when the utilization of each CPU cgroup is low and total
> utilization of all the CPU cgroup's is less than 50%. If the timers are
> interleaved, then the unthrottled cgroup can run freely without many
> context switches and can also benefit from SMT Folding. This effect will
> be further amplified in SPLPAR environment.
>
> This commit adds a random offset after initializing each hrtimer. This
> would result in interleaving the timers at expiry, which helps in achieving
> the said performance gain.
>
> This was tested on powerpc platform with 8 core SMT=8. Socket power was
> measured when the workload. Benchmarked the stress-ng with power
> information. Throughput oriented benchmarks show significant gain up to
> 25% while power consumption increases up to 15%.
>
> Workload: stress-ng --cpu=32 --cpu-ops=50000.
> 1CG - 1 cgroup is running.
> 2CG - 2 cgroups are running together.
> Time taken to complete stress-ng in seconds and power is in watts.
> each cgroup is throttled at 25% with 100ms as the period value.
> 6.2-rc6 | with patch
> 8 core 1CG power 2CG power | 1CG power 2 CG power
> 27.5 80.6 40 90 | 27.3 82 32.3 104
> 27.5 81 40.2 91 | 27.5 81 38.7 96
> 27.7 80 40.1 89 | 27.6 80 29.7 106
> 27.7 80.1 40.3 94 | 27.6 80 31.5 105
>
> Latency might be affected by this change. That could happen if the CPU was
> in a deep idle state which is possible if we interleave the timers. Used
> schbench for measuring the latency. Each cgroup is throttled at 25% with
> period value is set to 100ms. Numbers are when both the cgroups are
> running simultaneously. Latency values don't degrade much. Some
> improvement is seen in tail latencies.
>
> 6.2-rc6 with patch
> Groups: 16
> 50.0th: 39.5 42.5
> 75.0th: 924.0 922.0
> 90.0th: 972.0 968.0
> 95.0th: 1005.5 994.0
> 99.0th: 4166.0 2287.0
> 99.5th: 7314.0 7448.0
> 99.9th: 15024.0 13600.0
>
> Groups: 32
> 50.0th: 819.0 463.0
> 75.0th: 1596.0 918.0
> 90.0th: 5992.0 1281.5
> 95.0th: 13184.0 2765.0
> 99.0th: 21792.0 14240.0
> 99.5th: 25696.0 18920.0
> 99.9th: 33280.0 35776.0
>
> Groups: 64
> 50.0th: 4806.0 3440.0
> 75.0th: 31136.0 33664.0
> 90.0th: 54144.0 58752.0
> 95.0th: 66176.0 67200.0
> 99.0th: 84736.0 91520.0
> 99.5th: 97408.0 114048.0
> 99.9th: 136448.0 140032.0
>
> Signed-off-by: Shrikanth Hegde<[email protected]>
> Suggested-by: Peter Zijlstra <[email protected]>
> Suggested-by: Thomas Gleixner <[email protected]>
Reviewed-by: Ben Segall <[email protected]>
>
> Initial RFC PATCH, discussions and details on the problem:
> Link1: https://lore.kernel.org/lkml/[email protected]/
> Link2: https://lore.kernel.org/lkml/[email protected]/
>
> ---
> kernel/sched/fair.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index ff4dbbae3b10..2a4a0969e04f 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5923,6 +5923,10 @@ void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
> INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq);
> hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED);
> cfs_b->period_timer.function = sched_cfs_period_timer;
> +
> + /* Add a random offset so that timers interleave */
> + hrtimer_set_expires(&cfs_b->period_timer,
> + get_random_u32_below(cfs_b->period));
> hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> cfs_b->slack_timer.function = sched_cfs_slack_timer;
> cfs_b->slack_started = false;
> --
> 2.31.1
>> CPU cfs bandwidth controller uses hrtimer. Currently there is no initial
>> value set. Hence all period timers would align at expiry.
>> This happens when there are multiple CPU cgroup's.
>>
>> There is a performance gain that can be achieved here if the timers are
>> interleaved when the utilization of each CPU cgroup is low and total
>> utilization of all the CPU cgroup's is less than 50%. If the timers are
>> interleaved, then the unthrottled cgroup can run freely without many
>> context switches and can also benefit from SMT Folding. This effect will
>> be further amplified in SPLPAR environment.
>>
>> This commit adds a random offset after initializing each hrtimer. This
>> would result in interleaving the timers at expiry, which helps in achieving
>> the said performance gain.
>>
>> This was tested on powerpc platform with 8 core SMT=8. Socket power was
>> measured when the workload. Benchmarked the stress-ng with power
>> information. Throughput oriented benchmarks show significant gain up to
>> 25% while power consumption increases up to 15%.
>>
>> Workload: stress-ng --cpu=32 --cpu-ops=50000.
>> 1CG - 1 cgroup is running.
>> 2CG - 2 cgroups are running together.
>> Time taken to complete stress-ng in seconds and power is in watts.
>> each cgroup is throttled at 25% with 100ms as the period value.
>> 6.2-rc6 | with patch
>> 8 core 1CG power 2CG power | 1CG power 2 CG power
>> 27.5 80.6 40 90 | 27.3 82 32.3 104
>> 27.5 81 40.2 91 | 27.5 81 38.7 96
>> 27.7 80 40.1 89 | 27.6 80 29.7 106
>> 27.7 80.1 40.3 94 | 27.6 80 31.5 105
>>
>> Latency might be affected by this change. That could happen if the CPU was
>> in a deep idle state which is possible if we interleave the timers. Used
>> schbench for measuring the latency. Each cgroup is throttled at 25% with
>> period value is set to 100ms. Numbers are when both the cgroups are
>> running simultaneously. Latency values don't degrade much. Some
>> improvement is seen in tail latencies.
>>
>> 6.2-rc6 with patch
>> Groups: 16
>> 50.0th: 39.5 42.5
>> 75.0th: 924.0 922.0
>> 90.0th: 972.0 968.0
>> 95.0th: 1005.5 994.0
>> 99.0th: 4166.0 2287.0
>> 99.5th: 7314.0 7448.0
>> 99.9th: 15024.0 13600.0
>>
>> Groups: 32
>> 50.0th: 819.0 463.0
>> 75.0th: 1596.0 918.0
>> 90.0th: 5992.0 1281.5
>> 95.0th: 13184.0 2765.0
>> 99.0th: 21792.0 14240.0
>> 99.5th: 25696.0 18920.0
>> 99.9th: 33280.0 35776.0
>>
>> Groups: 64
>> 50.0th: 4806.0 3440.0
>> 75.0th: 31136.0 33664.0
>> 90.0th: 54144.0 58752.0
>> 95.0th: 66176.0 67200.0
>> 99.0th: 84736.0 91520.0
>> 99.5th: 97408.0 114048.0
>> 99.9th: 136448.0 140032.0
>>
>> Signed-off-by: Shrikanth Hegde<[email protected]>
>> Suggested-by: Peter Zijlstra <[email protected]>
>> Suggested-by: Thomas Gleixner <[email protected]>
>
> Reviewed-by: Ben Segall <[email protected]>
Ben, Thank you very much for the review.
Peter, Ingo, Vincent,
Could you please provide your inputs? Any other benchmarks should be run?
Sorry about the subject line. I should have included sched/fair. I realized it after
mail was sent. I sent another mail with only subject line changed.
They are same except subject line.
https://lore.kernel.org/lkml/[email protected]/
Should I resend the patch with better change log and a cover letter detailing
test results instead?
>
>>
>> Initial RFC PATCH, discussions and details on the problem:
>> Link1: https://lore.kernel.org/lkml/[email protected]/
>> Link2: https://lore.kernel.org/lkml/[email protected]/
>>
>> ---
>> kernel/sched/fair.c | 4 ++++
>> 1 file changed, 4 insertions(+)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index ff4dbbae3b10..2a4a0969e04f 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -5923,6 +5923,10 @@ void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
>> INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq);
>> hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED);
>> cfs_b->period_timer.function = sched_cfs_period_timer;
>> +
>> + /* Add a random offset so that timers interleave */
>> + hrtimer_set_expires(&cfs_b->period_timer,
>> + get_random_u32_below(cfs_b->period));
>> hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
>> cfs_b->slack_timer.function = sched_cfs_slack_timer;
>> cfs_b->slack_started = false;
>> --
>> 2.31.1
On Thu, 9 Mar 2023 at 15:22, Shrikanth Hegde <[email protected]> wrote:
>
>
>
> >> CPU cfs bandwidth controller uses hrtimer. Currently there is no initial
> >> value set. Hence all period timers would align at expiry.
> >> This happens when there are multiple CPU cgroup's.
> >>
> >> There is a performance gain that can be achieved here if the timers are
> >> interleaved when the utilization of each CPU cgroup is low and total
> >> utilization of all the CPU cgroup's is less than 50%. If the timers are
> >> interleaved, then the unthrottled cgroup can run freely without many
> >> context switches and can also benefit from SMT Folding. This effect will
> >> be further amplified in SPLPAR environment.
> >>
> >> This commit adds a random offset after initializing each hrtimer. This
> >> would result in interleaving the timers at expiry, which helps in achieving
> >> the said performance gain.
> >>
> >> This was tested on powerpc platform with 8 core SMT=8. Socket power was
> >> measured when the workload. Benchmarked the stress-ng with power
> >> information. Throughput oriented benchmarks show significant gain up to
> >> 25% while power consumption increases up to 15%.
> >>
> >> Workload: stress-ng --cpu=32 --cpu-ops=50000.
> >> 1CG - 1 cgroup is running.
> >> 2CG - 2 cgroups are running together.
> >> Time taken to complete stress-ng in seconds and power is in watts.
> >> each cgroup is throttled at 25% with 100ms as the period value.
> >> 6.2-rc6 | with patch
> >> 8 core 1CG power 2CG power | 1CG power 2 CG power
> >> 27.5 80.6 40 90 | 27.3 82 32.3 104
> >> 27.5 81 40.2 91 | 27.5 81 38.7 96
> >> 27.7 80 40.1 89 | 27.6 80 29.7 106
> >> 27.7 80.1 40.3 94 | 27.6 80 31.5 105
> >>
> >> Latency might be affected by this change. That could happen if the CPU was
> >> in a deep idle state which is possible if we interleave the timers. Used
> >> schbench for measuring the latency. Each cgroup is throttled at 25% with
> >> period value is set to 100ms. Numbers are when both the cgroups are
> >> running simultaneously. Latency values don't degrade much. Some
> >> improvement is seen in tail latencies.
> >>
> >> 6.2-rc6 with patch
> >> Groups: 16
> >> 50.0th: 39.5 42.5
> >> 75.0th: 924.0 922.0
> >> 90.0th: 972.0 968.0
> >> 95.0th: 1005.5 994.0
> >> 99.0th: 4166.0 2287.0
> >> 99.5th: 7314.0 7448.0
> >> 99.9th: 15024.0 13600.0
> >>
> >> Groups: 32
> >> 50.0th: 819.0 463.0
> >> 75.0th: 1596.0 918.0
> >> 90.0th: 5992.0 1281.5
> >> 95.0th: 13184.0 2765.0
> >> 99.0th: 21792.0 14240.0
> >> 99.5th: 25696.0 18920.0
> >> 99.9th: 33280.0 35776.0
> >>
> >> Groups: 64
> >> 50.0th: 4806.0 3440.0
> >> 75.0th: 31136.0 33664.0
> >> 90.0th: 54144.0 58752.0
> >> 95.0th: 66176.0 67200.0
> >> 99.0th: 84736.0 91520.0
> >> 99.5th: 97408.0 114048.0
> >> 99.9th: 136448.0 140032.0
> >>
> >> Signed-off-by: Shrikanth Hegde<[email protected]>
> >> Suggested-by: Peter Zijlstra <[email protected]>
> >> Suggested-by: Thomas Gleixner <[email protected]>
> >
> > Reviewed-by: Ben Segall <[email protected]>
Reviewed-by: Vincent Guittot <[email protected]>
>
> Ben, Thank you very much for the review.
>
> Peter, Ingo, Vincent,
> Could you please provide your inputs? Any other benchmarks should be run?
>
>
> Sorry about the subject line. I should have included sched/fair. I realized it after
> mail was sent. I sent another mail with only subject line changed.
> They are same except subject line.
> https://lore.kernel.org/lkml/[email protected]/
>
> Should I resend the patch with better change log and a cover letter detailing
> test results instead?
>
> >
> >>
> >> Initial RFC PATCH, discussions and details on the problem:
> >> Link1: https://lore.kernel.org/lkml/[email protected]/
> >> Link2: https://lore.kernel.org/lkml/[email protected]/
> >>
> >> ---
> >> kernel/sched/fair.c | 4 ++++
> >> 1 file changed, 4 insertions(+)
> >>
> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> >> index ff4dbbae3b10..2a4a0969e04f 100644
> >> --- a/kernel/sched/fair.c
> >> +++ b/kernel/sched/fair.c
> >> @@ -5923,6 +5923,10 @@ void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
> >> INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq);
> >> hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED);
> >> cfs_b->period_timer.function = sched_cfs_period_timer;
> >> +
> >> + /* Add a random offset so that timers interleave */
> >> + hrtimer_set_expires(&cfs_b->period_timer,
> >> + get_random_u32_below(cfs_b->period));
> >> hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> >> cfs_b->slack_timer.function = sched_cfs_slack_timer;
> >> cfs_b->slack_started = false;
> >> --
> >> 2.31.1
On Fri, Feb 24, 2023 at 12:21:53AM +0530, Shrikanth Hegde wrote:
> CPU cfs bandwidth controller uses hrtimer. Currently there is no initial
> value set. Hence all period timers would align at expiry.
> This happens when there are multiple CPU cgroup's.
>
> There is a performance gain that can be achieved here if the timers are
> interleaved when the utilization of each CPU cgroup is low and total
> utilization of all the CPU cgroup's is less than 50%. If the timers are
> interleaved, then the unthrottled cgroup can run freely without many
> context switches and can also benefit from SMT Folding. This effect will
> be further amplified in SPLPAR environment.
>
> This commit adds a random offset after initializing each hrtimer. This
> would result in interleaving the timers at expiry, which helps in achieving
> the said performance gain.
>
> This was tested on powerpc platform with 8 core SMT=8. Socket power was
> measured when the workload. Benchmarked the stress-ng with power
> information. Throughput oriented benchmarks show significant gain up to
> 25% while power consumption increases up to 15%.
>
> Workload: stress-ng --cpu=32 --cpu-ops=50000.
> 1CG - 1 cgroup is running.
> 2CG - 2 cgroups are running together.
> Time taken to complete stress-ng in seconds and power is in watts.
> each cgroup is throttled at 25% with 100ms as the period value.
> 6.2-rc6 | with patch
> 8 core 1CG power 2CG power | 1CG power 2 CG power
> 27.5 80.6 40 90 | 27.3 82 32.3 104
> 27.5 81 40.2 91 | 27.5 81 38.7 96
> 27.7 80 40.1 89 | 27.6 80 29.7 106
> 27.7 80.1 40.3 94 | 27.6 80 31.5 105
>
> Latency might be affected by this change. That could happen if the CPU was
> in a deep idle state which is possible if we interleave the timers. Used
> schbench for measuring the latency. Each cgroup is throttled at 25% with
> period value is set to 100ms. Numbers are when both the cgroups are
> running simultaneously. Latency values don't degrade much. Some
> improvement is seen in tail latencies.
>
> 6.2-rc6 with patch
> Groups: 16
> 50.0th: 39.5 42.5
> 75.0th: 924.0 922.0
> 90.0th: 972.0 968.0
> 95.0th: 1005.5 994.0
> 99.0th: 4166.0 2287.0
> 99.5th: 7314.0 7448.0
> 99.9th: 15024.0 13600.0
>
> Groups: 32
> 50.0th: 819.0 463.0
> 75.0th: 1596.0 918.0
> 90.0th: 5992.0 1281.5
> 95.0th: 13184.0 2765.0
> 99.0th: 21792.0 14240.0
> 99.5th: 25696.0 18920.0
> 99.9th: 33280.0 35776.0
>
> Groups: 64
> 50.0th: 4806.0 3440.0
> 75.0th: 31136.0 33664.0
> 90.0th: 54144.0 58752.0
> 95.0th: 66176.0 67200.0
> 99.0th: 84736.0 91520.0
> 99.5th: 97408.0 114048.0
> 99.9th: 136448.0 140032.0
>
> Signed-off-by: Shrikanth Hegde<[email protected]>
> Suggested-by: Peter Zijlstra <[email protected]>
> Suggested-by: Thomas Gleixner <[email protected]>
>
> Initial RFC PATCH, discussions and details on the problem:
> Link1: https://lore.kernel.org/lkml/[email protected]/
> Link2: https://lore.kernel.org/lkml/[email protected]/
Picked up for tip/sched/core.
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 41abdba9374734b743019fc1cc05e3225c82ba6b
Gitweb: https://git.kernel.org/tip/41abdba9374734b743019fc1cc05e3225c82ba6b
Author: Shrikanth Hegde <[email protected]>
AuthorDate: Fri, 24 Feb 2023 00:21:53 +05:30
Committer: Peter Zijlstra <[email protected]>
CommitterDate: Wed, 22 Mar 2023 10:10:58 +01:00
sched: Interleave cfs bandwidth timers for improved single thread performance at low utilization
CPU cfs bandwidth controller uses hrtimer. Currently there is no initial
value set. Hence all period timers would align at expiry.
This happens when there are multiple CPU cgroup's.
There is a performance gain that can be achieved here if the timers are
interleaved when the utilization of each CPU cgroup is low and total
utilization of all the CPU cgroup's is less than 50%. If the timers are
interleaved, then the unthrottled cgroup can run freely without many
context switches and can also benefit from SMT Folding. This effect will
be further amplified in SPLPAR environment.
This commit adds a random offset after initializing each hrtimer. This
would result in interleaving the timers at expiry, which helps in achieving
the said performance gain.
This was tested on powerpc platform with 8 core SMT=8. Socket power was
measured when the workload. Benchmarked the stress-ng with power
information. Throughput oriented benchmarks show significant gain up to
25% while power consumption increases up to 15%.
Workload: stress-ng --cpu=32 --cpu-ops=50000.
1CG - 1 cgroup is running.
2CG - 2 cgroups are running together.
Time taken to complete stress-ng in seconds and power is in watts.
each cgroup is throttled at 25% with 100ms as the period value.
6.2-rc6 | with patch
8 core 1CG power 2CG power | 1CG power 2 CG power
27.5 80.6 40 90 | 27.3 82 32.3 104
27.5 81 40.2 91 | 27.5 81 38.7 96
27.7 80 40.1 89 | 27.6 80 29.7 106
27.7 80.1 40.3 94 | 27.6 80 31.5 105
Latency might be affected by this change. That could happen if the CPU was
in a deep idle state which is possible if we interleave the timers. Used
schbench for measuring the latency. Each cgroup is throttled at 25% with
period value is set to 100ms. Numbers are when both the cgroups are
running simultaneously. Latency values don't degrade much. Some
improvement is seen in tail latencies.
6.2-rc6 with patch
Groups: 16
50.0th: 39.5 42.5
75.0th: 924.0 922.0
90.0th: 972.0 968.0
95.0th: 1005.5 994.0
99.0th: 4166.0 2287.0
99.5th: 7314.0 7448.0
99.9th: 15024.0 13600.0
Groups: 32
50.0th: 819.0 463.0
75.0th: 1596.0 918.0
90.0th: 5992.0 1281.5
95.0th: 13184.0 2765.0
99.0th: 21792.0 14240.0
99.5th: 25696.0 18920.0
99.9th: 33280.0 35776.0
Groups: 64
50.0th: 4806.0 3440.0
75.0th: 31136.0 33664.0
90.0th: 54144.0 58752.0
95.0th: 66176.0 67200.0
99.0th: 84736.0 91520.0
99.5th: 97408.0 114048.0
99.9th: 136448.0 140032.0
Initial RFC PATCH, discussions and details on the problem:
Link1: https://lore.kernel.org/lkml/[email protected]/
Link2: https://lore.kernel.org/lkml/[email protected]/
Suggested-by: Peter Zijlstra <[email protected]>
Suggested-by: Thomas Gleixner <[email protected]>
Signed-off-by: Shrikanth Hegde<[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Ben Segall <[email protected]>
Reviewed-by: Vincent Guittot <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
kernel/sched/fair.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b572367..bc358dc 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5923,6 +5923,10 @@ void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq);
hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED);
cfs_b->period_timer.function = sched_cfs_period_timer;
+
+ /* Add a random offset so that timers interleave */
+ hrtimer_set_expires(&cfs_b->period_timer,
+ get_random_u32_below(cfs_b->period));
hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
cfs_b->slack_timer.function = sched_cfs_slack_timer;
cfs_b->slack_started = false;