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Date: Thu, 27 Jan 2022 11:05:52 +0800
From: Yicong Yang <yangyicong@...wei.com>
To: Tim Chen <tim.c.chen@...ux.intel.com>,
Yicong Yang <yangyicong@...ilicon.com>, <peterz@...radead.org>,
<mingo@...hat.com>, <juri.lelli@...hat.com>,
<vincent.guittot@...aro.org>, <gautham.shenoy@....com>,
<linux-kernel@...r.kernel.org>,
<linux-arm-kernel@...ts.infradead.org>
CC: <dietmar.eggemann@....com>, <rostedt@...dmis.org>,
<bsegall@...gle.com>, <bristot@...hat.com>,
<prime.zeng@...wei.com>, <jonathan.cameron@...wei.com>,
<ego@...ux.vnet.ibm.com>, <srikar@...ux.vnet.ibm.com>,
<linuxarm@...wei.com>, <21cnbao@...il.com>,
<song.bao.hua@...ilicon.com>, <guodong.xu@...aro.org>
Subject: Re: [PATCH v2 2/2] sched/fair: Scan cluster before scanning LLC in
wake-up path
On 2022/1/27 10:36, Tim Chen wrote:
> On Wed, 2022-01-26 at 18:30 -0800, Tim Chen wrote:
>> On Thu, 2022-01-27 at 10:02 +0800, Yicong Yang wrote:
>>> 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@...ilicon.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@...ilicon.com>
>>>>> Signed-off-by: Barry Song <song.bao.hua@...ilicon.com>
>>>>> Signed-off-by: Yicong Yang <yangyicong@...ilicon.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.
>>
>> Ah, I missed the fact that cpus point to the select_idle_mask.
>>
>
> I think it will be easier to read the code if you pass "cpus" directly
> to scan cluster, rather than making this implicit, and having this
> assignment
>
> *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
>
> again in scan_cluster.
sure. It does look more readable and I think we can change to that. :)
Thanks.
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