[PATCH v2 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path
Yicong Yang
yangyicong at huawei.com
Wed Jan 26 18:02:37 PST 2022
On 2022/1/27 9:14, Tim Chen wrote:
> On Wed, 2022-01-26 at 16:09 +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:
>> 5.17-rc1 patched
>> Hmean 1 324.73 ( 0.00%) 378.01 * 16.41%*
>> Hmean 2 645.36 ( 0.00%) 754.63 * 16.93%*
>> Hmean 4 1302.09 ( 0.00%) 1507.54 * 15.78%*
>> Hmean 8 2612.03 ( 0.00%) 2982.57 * 14.19%*
>> Hmean 16 5307.12 ( 0.00%) 5886.66 * 10.92%*
>> Hmean 32 9354.22 ( 0.00%) 9908.13 * 5.92%*
>> Hmean 64 7240.35 ( 0.00%) 7278.78 * 0.53%*
>> Hmean 128 6186.40 ( 0.00%) 6187.85 ( 0.02%)
>>
>> On numa 0-1:
>> 5.17-rc1 patched
>> Hmean 1 320.01 ( 0.00%) 378.44 * 18.26%*
>> Hmean 2 643.85 ( 0.00%) 752.52 * 16.88%*
>> Hmean 4 1287.36 ( 0.00%) 1505.62 * 16.95%*
>> Hmean 8 2564.60 ( 0.00%) 2955.29 * 15.23%*
>> Hmean 16 5195.69 ( 0.00%) 5814.74 * 11.91%*
>> Hmean 32 9769.16 ( 0.00%) 10872.63 * 11.30%*
>> Hmean 64 15952.50 ( 0.00%) 17281.98 * 8.33%*
>> Hmean 128 13113.77 ( 0.00%) 13895.20 * 5.96%*
>> Hmean 256 10997.59 ( 0.00%) 11244.69 * 2.25%*
>> Hmean 512 14623.60 ( 0.00%) 15526.25 * 6.17%*
>>
>> This will also help to improve the MySQL. With MySQL server
>> running on numa 0 and client running on numa 1, both QPS and
>> latency is imporved on read-write case:
>> 5.17-rc1 patched
>> QPS-16threads 143333.2633 145077.4033(+1.22%)
>> QPS-24threads 195085.9367 202719.6133(+3.91%)
>> QPS-32threads 241165.6867 249020.74(+3.26%)
>> QPS-64threads 244586.8433 253387.7567(+3.60%)
>> avg-lat-16threads 2.23 2.19(+1.19%)
>> avg-lat-24threads 2.46 2.36(+3.79%)
>> avg-lat-36threads 2.66 2.57(+3.26%)
>> avg-lat-64threads 5.23 5.05(+3.44%)
>>
>> 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 | 46 +++++++++++++++++++++++++++++++++++++++++
>> ----
>> 1 file changed, 42 insertions(+), 4 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 5146163bfabb..2f84a933aedd 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -6262,12 +6262,46 @@ 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, int prev_cpu,
>> int target)
>> +{
>> + struct cpumask *cpus =
>> this_cpu_cpumask_var_ptr(select_idle_mask);
>> + struct sched_domain *sd = rcu_dereference(per_cpu(sd_cluster,
>> target));
>> + int cpu, idle_cpu;
>> +
>> + /* TODO: Support SMT case while a machine with both cluster and
>> SMT born */
>
> This is probably a clearer comment
>
> /* TODO: Support SMT system with cluster topology */
>
>> + if (!sched_smt_active() && sd) {
>> + for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) {
>> + idle_cpu = __select_idle_cpu(cpu, p);
>> */
>> -static int select_idle_cpu(struct task_struct *p, struct
>> sched_domain *sd, bool has_idle_core, int target)
>> +static int select_idle_cpu(struct task_struct *p, struct
>> sched_domain *sd, bool has_idle_core, int prev_cpu, int target)
>> {
>> struct cpumask *cpus =
>> this_cpu_cpumask_var_ptr(select_idle_mask);
>> int i, cpu, idle_cpu = -1, nr = INT_MAX;
>> @@ -6282,6 +6316,10 @@ static int select_idle_cpu(struct task_struct
>> *p, struct sched_domain *sd, bool
>>
>> cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
>>
>> + idle_cpu = scan_cluster(p, prev_cpu, target);
>
> Shouldn't "cpus" from
>
> cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
>
> be passed to scan_cluster, to make sure that the cpu returned is
> in the affinity mask of the task? I don't see p->cpus_ptr
> being checked in scan_cluster to make sure the cpu found is in the
> affinity mask.
>
The cpus scanned in scan_cluster() is the intersection of
select_idle_mask and sched_domain_span(cluster_sd), and
we limited the select_idle_mask in the tasks' affinity mask
before we enter scan_cluster() here.
Thanks.
> Tim
>
>
>> + if ((unsigned int)idle_cpu < nr_cpumask_bits)
>> + return idle_cpu;
>> +
>> if (sched_feat(SIS_PROP) && !has_idle_core) {
>> u64 avg_cost, avg_idle, span_avg;
>> unsigned long now = jiffies;
>> @@ -6416,7 +6454,7 @@ 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;
>> @@ -6442,7 +6480,7 @@ 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)) {
>> @@ -6483,7 +6521,7 @@ static int select_idle_sibling(struct
>> task_struct *p, int prev, int target)
>> }
>> }
>>
>> - i = select_idle_cpu(p, sd, has_idle_core, target);
>> + i = select_idle_cpu(p, sd, has_idle_core, prev, target);
>> if ((unsigned)i < nr_cpumask_bits)
>> return i;
>>
>
> .
>
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