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Message-ID: <3105c9d4-9707-e9a3-47e5-c63095fa46e2@huawei.com>
Date: Mon, 27 Jun 2022 16:16:33 +0800
From: Yicong Yang <yangyicong@...wei.com>
To: Abel Wu <wuyun.abel@...edance.com>,
Yicong Yang <yangyicong@...ilicon.com>, <peterz@...radead.org>,
<mingo@...hat.com>, <juri.lelli@...hat.com>,
<vincent.guittot@...aro.org>, <tim.c.chen@...ux.intel.com>,
<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>,
<guodong.xu@...aro.org>, <hesham.almatary@...wei.com>,
<john.garry@...wei.com>, <shenyang39@...wei.com>
Subject: Re: [PATCH v4 2/2] sched/fair: Scan cluster before scanning LLC in
wake-up path
On 2022/6/26 20:13, Abel Wu wrote:
>
> On 6/9/22 8:06 PM, 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:
>> 5.19-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%*
>>
>> 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 | 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;
>
> return -1;
> :)
>
thanks for the comment. If we've run out of nr the select_idle_cpu() will stop scanning as well,
so it's unnecessary to clear the mask of cluster cpus and just return.
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