[PATCH v4 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path
Yicong Yang
yangyicong at huawei.com
Thu Jun 9 23:39:38 PDT 2022
On 2022/6/10 6:47, Tim Chen wrote:
> On Thu, 2022-06-09 at 20:06 +0800, Yicong Yang wrote:
>> From: Barry Song <song.bao.hua at hisilicon.com>
>>
>> For platforms having clusters like Kunpeng920, CPUs within the same cluster
>> have lower latency when synchronizing and accessing shared resources like
>> cache. Thus, this patch tries to find an idle cpu within the cluster of the
>> target CPU before scanning the whole LLC to gain lower latency.
>>
>> Note neither Kunpeng920 nor x86 Jacobsville supports SMT, so this patch
>> doesn't consider SMT for this moment.
>>
>> Testing has been done on Kunpeng920 by pinning tasks to one numa and two
>> numa. On Kunpeng920, Each numa has 8 clusters and each cluster has 4 CPUs.
>>
>> With this patch, We noticed enhancement on tbench within one numa or cross
>> two numa.
>>
>> On numa 0:
>> 5.19-rc1 patched
>> Hmean 1 350.27 ( 0.00%) 406.88 * 16.16%*
>> Hmean 2 702.01 ( 0.00%) 808.22 * 15.13%*
>> Hmean 4 1405.14 ( 0.00%) 1614.34 * 14.89%*
>> Hmean 8 2830.53 ( 0.00%) 3169.02 * 11.96%*
>> Hmean 16 5597.95 ( 0.00%) 6224.20 * 11.19%*
>> Hmean 32 10537.38 ( 0.00%) 10524.97 * -0.12%*
>> Hmean 64 8366.04 ( 0.00%) 8437.41 * 0.85%*
>> Hmean 128 7060.87 ( 0.00%) 7150.25 * 1.27%*
>>
>> On numa 0-1:
>> 5.19-rc1 patched
>> Hmean 1 346.11 ( 0.00%) 408.47 * 18.02%*
>> Hmean 2 693.34 ( 0.00%) 805.78 * 16.22%*
>> Hmean 4 1384.96 ( 0.00%) 1602.49 * 15.71%*
>> Hmean 8 2699.45 ( 0.00%) 3069.98 * 13.73%*
>> Hmean 16 5327.11 ( 0.00%) 5688.19 * 6.78%*
>> Hmean 32 10019.10 ( 0.00%) 11862.56 * 18.40%*
>> Hmean 64 13850.57 ( 0.00%) 17748.54 * 28.14%*
>> Hmean 128 12498.25 ( 0.00%) 15541.59 * 24.35%*
>> Hmean 256 11195.77 ( 0.00%) 13854.06 * 23.74%*
>
> Yicong,
>
> Have you tried any workload where tasks don't share data
> with each other but have sleep/wakeup? That's the case
> where we actually want to spread the tasks out among the clusters
> to void contention for L2 cache.
>
> Will be nice to make sure there's no regression there for
> such workload.
>
Any certain workload you'd like me test? I'm willing to do :)
I've tested this patch with MySQL as well (like in v2). This won't hurt
the MySQL case with SIS_PROP but observed some improvement with SIS_UTIL
posted in [1]. We leverage the nr to suppress redundant scanning in the
current approach and seems SIS_UTIL is more efficient in this case.
5.19-rc1 patched patched+SIS_UTIL[1]
TPS-16threads 6215.11 6172.74 (-0.68%) 6217.33 (0.04%)
QPS-16threads 124302.21 123454.68 (-0.68%) 124346.52 (0.04%)
avg-lat-16threads 2.57 2.59 (-0.65%) 2.57 (0.00%)
TPS-24threads 8726.40 8690.87 (-0.41%) 8833.08 (1.22%)
QPS-24threads 174527.88 173817.42 (-0.41%) 176661.54 (1.21%)
avg-lat-24threads 2.75 2.76 (-0.36%) 2.71 (1.33%)
TPS-32threads 9555.42 9514.86 (-0.42%) 10010.87 (4.77%)
QPS-32threads 191108.37 190297.28 (-0.42%) 200217.35 (4.55%)
avg-lat-32threads 3.35 3.36 (-0.30%) 3.20 (4.58%)
TPS-64threads 10290.10 10324.75 (0.34%) 10819.77 (5.15%)
QPS-64threads 205802.05 206494.95 (0.34%) 216395.40 (4.90%)
avg-lat-64threads 6.22 6.20 (0.38%) 5.92 (4.88%)
> Code itself looks good.
>
> Reviewed-by: Tim Chen <tim.c.chen at linux.intel.com>
>
Thanks.
[1] https://lore.kernel.org/lkml/20220428182442.659294-1-yu.c.chen@intel.com/
>>
>> Tested-by: Yicong Yang <yangyicong at hisilicon.com>
>> Signed-off-by: Barry Song <song.bao.hua at hisilicon.com>
>> Signed-off-by: Yicong Yang <yangyicong at hisilicon.com>
>> ---
>> kernel/sched/fair.c | 44 +++++++++++++++++++++++++++++++++++++++++---
>> 1 file changed, 41 insertions(+), 3 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 77b2048a9326..6d173e196ad3 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -6327,6 +6327,40 @@ static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd
>>
>> #endif /* CONFIG_SCHED_SMT */
>>
>> +#ifdef CONFIG_SCHED_CLUSTER
>> +/*
>> + * Scan the cluster domain for idle CPUs and clear cluster cpumask after scanning
>> + */
>> +static inline int scan_cluster(struct task_struct *p, struct cpumask *cpus,
>> + int target, int *nr)
>> +{
>> + struct sched_domain *sd = rcu_dereference(per_cpu(sd_cluster, target));
>> + int cpu, idle_cpu;
>> +
>> + /* TODO: Support SMT system with cluster topology */
>> + if (!sched_smt_active() && sd) {
>> + for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) {
>> + if (!--*nr)
>> + break;
>> +
>> + idle_cpu = __select_idle_cpu(cpu, p);
>> + if ((unsigned int)idle_cpu < nr_cpumask_bits)
>> + return idle_cpu;
>> + }
>> +
>> + cpumask_andnot(cpus, cpus, sched_domain_span(sd));
>> + }
>> +
>> + return -1;
>> +}
>> +#else
>> +static inline int scan_cluster(struct task_struct *p, struct cpumask *cpus,
>> + int target, int *nr)
>> +{
>> + return -1;
>> +}
>> +#endif
>> +
>> /*
>> * Scan the LLC domain for idle CPUs; this is dynamically regulated by
>> * comparing the average scan cost (tracked in sd->avg_scan_cost) against the
>> @@ -6375,6 +6409,10 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
>> time = cpu_clock(this);
>> }
>>
>> + idle_cpu = scan_cluster(p, cpus, target, &nr);
>> + if ((unsigned int)idle_cpu < nr_cpumask_bits)
>> + return idle_cpu;
>> +
>> for_each_cpu_wrap(cpu, cpus, target + 1) {
>> if (has_idle_core) {
>> i = select_idle_core(p, cpu, cpus, &idle_cpu);
>> @@ -6382,7 +6420,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
>> return i;
>>
>> } else {
>> - if (!--nr)
>> + if (--nr <= 0)
>> return -1;
>> idle_cpu = __select_idle_cpu(cpu, p);
>> if ((unsigned int)idle_cpu < nr_cpumask_bits)
>> @@ -6481,7 +6519,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
>> /*
>> * If the previous CPU is cache affine and idle, don't be stupid:
>> */
>> - if (prev != target && cpus_share_cache(prev, target) &&
>> + if (prev != target && cpus_share_resources(prev, target) &&
>> (available_idle_cpu(prev) || sched_idle_cpu(prev)) &&
>> asym_fits_capacity(task_util, prev))
>> return prev;
>> @@ -6507,7 +6545,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
>> p->recent_used_cpu = prev;
>> if (recent_used_cpu != prev &&
>> recent_used_cpu != target &&
>> - cpus_share_cache(recent_used_cpu, target) &&
>> + cpus_share_resources(recent_used_cpu, target) &&
>> (available_idle_cpu(recent_used_cpu) || sched_idle_cpu(recent_used_cpu)) &&
>> cpumask_test_cpu(p->recent_used_cpu, p->cpus_ptr) &&
>> asym_fits_capacity(task_util, recent_used_cpu)) {
>
>
> .
>
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