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Date: Thu, 14 Jul 2022 00:14:29 +0800
From: Abel Wu <wuyun.abel@...edance.com>
To: Chen Yu <yu.c.chen@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Mel Gorman <mgorman@...e.de>,
Vincent Guittot <vincent.guittot@...aro.org>,
Josh Don <joshdon@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] sched/fair: ignore SIS_UTIL when has idle core
On 7/13/22 11:47 AM, Chen Yu Wrote:
> On Tue, Jul 12, 2022 at 04:20:32PM +0800, Abel Wu wrote:
>> When SIS_UTIL is enabled, SIS domain scan will be skipped if
>> the LLC is overloaded. Since the overloaded status is checked
>> in the load balancing at LLC level, the interval is llc_size
>> miliseconds. The duration might be long enough to affect the
>> overall system throughput if idle cores are out of reach in
>> SIS domain scan.
> The idle core scan was skipped in SIS_UTIL because we saw better
> improvement in some benchmarks. But yes, we could make has_idle_core
> to scan anyway no matter what the system load is, if we have some
> data to support it. I'll test this patch on top of latest sched/core
> branch to see if this makes a difference.
I did some benchmark in my machine: netperf showed ~3% regression
and considerable improvement in hackbench pipe.
Maybe there are some workload benefit from selecting the recent
cpus rather than idle ones, but I don't think the recent_cpu can
out-perform the idle core much, since the two cpus still share
LLC cache and idle core has more capacity than idle cpu. Besides
this case, idle cores usually are better choices I think. So it
might worth a full scan if idle cores are available.
Thanks,
Abel
-------8<---
Tests are done in an Intel Xeon(R) Platinum 8260 CPU@...0GHz machine
with 2 NUMA nodes each of which has 24 cores with SMT2 enabled, so 96
CPUs in total.
All of the benchmarks are done inside a normal cpu cgroup in a clean
environment with cpu turbo disabled.
Based on tip sched/core c02d5546ea34 (v5.19-rc2).
1) hackbench-process-pipes
Amean 1 0.2307 ( 0.00%) 0.2277 ( 1.30%)
Amean 4 0.6277 ( 0.00%) 0.6037 ( 3.82%)
Amean 7 0.7897 ( 0.00%) 0.7710 * 2.36%*
Amean 12 1.2067 ( 0.00%) 1.3087 ( -8.45%)
Amean 21 2.6717 ( 0.00%) 2.5077 ( 6.14%)
Amean 30 5.0893 ( 0.00%) 3.9610 ( 22.17%)
Amean 48 9.2407 ( 0.00%) 7.4030 * 19.89%*
Amean 79 9.5607 ( 0.00%) 9.3960 ( 1.72%)
Amean 110 10.6053 ( 0.00%) 10.6453 ( -0.38%)
Amean 141 12.8210 ( 0.00%) 12.5253 ( 2.31%)
Amean 172 14.9777 ( 0.00%) 14.4317 ( 3.65%)
Amean 203 18.1320 ( 0.00%) 16.9753 * 6.38%*
Amean 234 20.1207 ( 0.00%) 19.0730 * 5.21%*
Amean 265 22.7037 ( 0.00%) 21.7953 ( 4.00%)
Amean 296 25.6753 ( 0.00%) 23.6877 * 7.74%*
2) hackbench-process-sockets
Amean 1 0.4223 ( 0.00%) 0.4300 ( -1.82%)
Amean 4 1.4470 ( 0.00%) 1.4593 * -0.85%*
Amean 7 2.4803 ( 0.00%) 2.4843 ( -0.16%)
Amean 12 4.1457 ( 0.00%) 4.1170 * 0.69%*
Amean 21 7.0223 ( 0.00%) 7.0053 ( 0.24%)
Amean 30 9.9570 ( 0.00%) 9.8683 * 0.89%*
Amean 48 16.0213 ( 0.00%) 15.6657 * 2.22%*
Amean 79 26.8140 ( 0.00%) 26.3657 * 1.67%*
Amean 110 37.3530 ( 0.00%) 36.8800 * 1.27%*
Amean 141 47.6123 ( 0.00%) 47.1627 ( 0.94%)
Amean 172 57.6757 ( 0.00%) 57.1430 * 0.92%*
Amean 203 68.2310 ( 0.00%) 67.6030 ( 0.92%)
Amean 234 78.1990 ( 0.00%) 77.7073 * 0.63%*
Amean 265 88.9657 ( 0.00%) 87.9833 * 1.10%*
Amean 296 99.8617 ( 0.00%) 98.1073 * 1.76%*
3) hackbench-thread-pipes
Amean 1 0.2650 ( 0.00%) 0.2807 ( -5.91%)
Amean 4 0.6650 ( 0.00%) 0.6257 * 5.91%*
Amean 7 0.8283 ( 0.00%) 0.8207 ( 0.93%)
Amean 12 1.3343 ( 0.00%) 1.3050 ( 2.20%)
Amean 21 3.7053 ( 0.00%) 2.7530 * 25.70%*
Amean 30 7.2817 ( 0.00%) 4.2013 * 42.30%*
Amean 48 9.9037 ( 0.00%) 8.8483 * 10.66%*
Amean 79 10.0790 ( 0.00%) 10.1603 ( -0.81%)
Amean 110 11.5837 ( 0.00%) 11.1297 ( 3.92%)
Amean 141 13.4760 ( 0.00%) 12.9903 ( 3.60%)
Amean 172 16.2357 ( 0.00%) 15.5903 ( 3.97%)
Amean 203 18.2873 ( 0.00%) 17.8690 ( 2.29%)
Amean 234 21.2920 ( 0.00%) 20.4680 ( 3.87%)
Amean 265 23.9393 ( 0.00%) 22.3933 * 6.46%*
Amean 296 26.6683 ( 0.00%) 26.1260 ( 2.03%)
4) hackbench-thread-sockets
Amean 1 0.4700 ( 0.00%) 0.4437 ( 5.60%)
Amean 4 1.4837 ( 0.00%) 1.4960 ( -0.83%)
Amean 7 2.5497 ( 0.00%) 2.5240 * 1.01%*
Amean 12 4.2473 ( 0.00%) 4.2137 * 0.79%*
Amean 21 7.2530 ( 0.00%) 7.1800 * 1.01%*
Amean 30 10.1973 ( 0.00%) 10.1483 ( 0.48%)
Amean 48 16.2163 ( 0.00%) 16.0870 * 0.80%*
Amean 79 27.4460 ( 0.00%) 27.0770 * 1.34%*
Amean 110 38.1103 ( 0.00%) 37.5573 * 1.45%*
Amean 141 48.4513 ( 0.00%) 48.0347 ( 0.86%)
Amean 172 59.4410 ( 0.00%) 58.4020 * 1.75%*
Amean 203 70.0873 ( 0.00%) 69.0470 * 1.48%*
Amean 234 80.3570 ( 0.00%) 79.4163 * 1.17%*
Amean 265 91.8550 ( 0.00%) 90.3417 * 1.65%*
Amean 296 102.7420 ( 0.00%) 100.8933 * 1.80%*
5) netperf-udp
Hmean send-64 210.14 ( 0.00%) 202.26 * -3.75%*
Hmean send-128 418.23 ( 0.00%) 404.14 * -3.37%*
Hmean send-256 821.31 ( 0.00%) 789.94 * -3.82%*
Hmean send-1024 3161.96 ( 0.00%) 3025.23 * -4.32%*
Hmean send-2048 5959.67 ( 0.00%) 5725.35 * -3.93%*
Hmean send-3312 9196.99 ( 0.00%) 8830.47 * -3.99%*
Hmean send-4096 11061.30 ( 0.00%) 10675.83 * -3.48%*
Hmean send-8192 17320.16 ( 0.00%) 17601.11 * 1.62%*
Hmean send-16384 27936.12 ( 0.00%) 27859.52 ( -0.27%)
Hmean recv-64 210.14 ( 0.00%) 202.26 * -3.75%*
Hmean recv-128 418.23 ( 0.00%) 404.14 * -3.37%*
Hmean recv-256 821.31 ( 0.00%) 789.94 * -3.82%*
Hmean recv-1024 3161.95 ( 0.00%) 3025.23 * -4.32%*
Hmean recv-2048 5959.44 ( 0.00%) 5725.35 * -3.93%*
Hmean recv-3312 9196.99 ( 0.00%) 8830.44 * -3.99%*
Hmean recv-4096 11061.26 ( 0.00%) 10675.83 * -3.48%*
Hmean recv-8192 17319.62 ( 0.00%) 17601.10 * 1.63%*
Hmean recv-16384 27935.00 ( 0.00%) 27859.40 ( -0.27%)
6) netperf-tcp
Hmean 64 1222.35 ( 0.00%) 1195.62 * -2.19%*
Hmean 128 2372.82 ( 0.00%) 2311.15 * -2.60%*
Hmean 256 4305.82 ( 0.00%) 4244.00 ( -1.44%)
Hmean 1024 13645.83 ( 0.00%) 13299.13 * -2.54%*
Hmean 2048 21119.56 ( 0.00%) 21042.51 ( -0.36%)
Hmean 3312 24835.87 ( 0.00%) 25282.73 * 1.80%*
Hmean 4096 26705.57 ( 0.00%) 26851.09 ( 0.54%)
Hmean 8192 30889.25 ( 0.00%) 31436.74 * 1.77%*
Hmean 16384 35108.55 ( 0.00%) 35172.76 ( 0.18%)
7) tbench4 Throughput
Hmean 1 289.23 ( 0.00%) 289.58 ( 0.12%)
Hmean 2 577.35 ( 0.00%) 576.40 * -0.17%*
Hmean 4 1141.02 ( 0.00%) 1155.58 * 1.28%*
Hmean 8 2258.36 ( 0.00%) 2287.82 * 1.30%*
Hmean 16 4410.02 ( 0.00%) 4510.76 * 2.28%*
Hmean 32 7414.89 ( 0.00%) 7474.74 * 0.81%*
Hmean 64 9011.49 ( 0.00%) 8973.50 * -0.42%*
Hmean 128 19892.18 ( 0.00%) 19913.82 * 0.11%*
Hmean 256 19854.73 ( 0.00%) 20239.21 * 1.94%*
Hmean 384 19808.80 ( 0.00%) 19709.59 * -0.50%*
>
> thanks,
> Chenyu
>>
>> Signed-off-by: Abel Wu <wuyun.abel@...edance.com>
>> ---
>> kernel/sched/fair.c | 15 +++++++++------
>> 1 file changed, 9 insertions(+), 6 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index a78d2e3b9d49..cd758b3616bd 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -6392,16 +6392,19 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
>> struct sched_domain *this_sd;
>> u64 time = 0;
>>
>> - this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
>> - if (!this_sd)
>> - return -1;
>> -
>> cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
>>
>> - if (sched_feat(SIS_PROP) && !has_idle_core) {
>> + if (has_idle_core)
>> + goto scan;
>> +
>> + if (sched_feat(SIS_PROP)) {
>> u64 avg_cost, avg_idle, span_avg;
>> unsigned long now = jiffies;
>>
>> + this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
>> + if (!this_sd)
>> + return -1;
>> +
>> /*
>> * If we're busy, the assumption that the last idle period
>> * predicts the future is flawed; age away the remaining
>> @@ -6436,7 +6439,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
>> return -1;
>> }
>> }
>> -
>> +scan:
>> for_each_cpu_wrap(cpu, cpus, target + 1) {
>> if (has_idle_core) {
>> i = select_idle_core(p, cpu, cpus, &idle_cpu);
>> --
>> 2.31.1
>>
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