From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3CBE3C43334 for ; Thu, 14 Jul 2022 08:17:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231339AbiGNIRV (ORCPT ); Thu, 14 Jul 2022 04:17:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40584 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234349AbiGNIQ7 (ORCPT ); Thu, 14 Jul 2022 04:16:59 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 760731DA62 for ; Thu, 14 Jul 2022 01:16:57 -0700 (PDT) Received: from canpemm500009.china.huawei.com (unknown [172.30.72.54]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4Lk6gW5Yk1zVfbn; Thu, 14 Jul 2022 16:13:11 +0800 (CST) Received: from [10.67.102.169] (10.67.102.169) by canpemm500009.china.huawei.com (7.192.105.203) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 14 Jul 2022 16:16:54 +0800 CC: , Josh Don , Chen Yu , Subject: Re: [PATCH 1/5] sched/fair: ignore SIS_UTIL when has idle core To: Abel Wu , Peter Zijlstra , Mel Gorman , Vincent Guittot References: <20220712082036.5130-1-wuyun.abel@bytedance.com> <20220712082036.5130-2-wuyun.abel@bytedance.com> <8e7d75d4-613e-f35e-e932-323789666fb1@huawei.com> <4dde05be-8470-5984-0a30-ba077b9fe6bd@bytedance.com> <5df03ae2-6c5d-aa38-4a4d-632c0f484140@bytedance.com> From: Yicong Yang Message-ID: Date: Thu, 14 Jul 2022 16:16:54 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: <5df03ae2-6c5d-aa38-4a4d-632c0f484140@bytedance.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.67.102.169] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To canpemm500009.china.huawei.com (7.192.105.203) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/7/14 16:00, Abel Wu wrote: > > On 7/14/22 3:15 PM, Yicong Yang Wrote: >> On 2022/7/14 14:58, Abel Wu wrote: >>> >>> On 7/14/22 2:19 PM, Yicong Yang Wrote: >>>> On 2022/7/12 16:20, 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. >>>>> >>>>> Signed-off-by: Abel Wu >>>>> --- >>>>>    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; >>>>> + >>>> >>>> I don't follow the change here. True that this_sd is used only in SIS_PROP, but it seems irrelevant with your >>>> commit. Does the position of this make any performance difference? >>> >>> No, this change doesn't make much difference to performance. Are >>> you suggesting that I should make this a separate patch? >>> >> >> It just makes me think that dereference is unnecessary if this_cpu and target locates in >> the same LLC, since it's already been passed. But since you noticed no difference it may >> have little effect. :) >> > > Hmm.. Not exactly. The sched-domains are cpu private, and this_cpu can > be in another LLC than target. > . yes. you're right. sorry for get this messed.