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 X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B35F8C2D0BF for ; Tue, 10 Dec 2019 09:44:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 80C9720663 for ; Tue, 10 Dec 2019 09:44:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="M3jycdht" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727143AbfLJJoC (ORCPT ); Tue, 10 Dec 2019 04:44:02 -0500 Received: from mail-lf1-f66.google.com ([209.85.167.66]:33646 "EHLO mail-lf1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727083AbfLJJoC (ORCPT ); Tue, 10 Dec 2019 04:44:02 -0500 Received: by mail-lf1-f66.google.com with SMTP id n25so13212494lfl.0 for ; Tue, 10 Dec 2019 01:43:59 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=eVprmkX04/ZA2Ox8rlDXhtYrH8Cdrulho+SeNeN/8to=; b=M3jycdhtLFPex3L2spBWypQ+mK6nzf31bl4Gqd6sV7LltjwgcUk+7tKuPRbipf0QT8 DUdNjLvxx+OlIZd/SEXYZwssHKB/+1igQw9UrcPIS1qNYoNdnTC+BuYqHJpWChzAQPu2 C1lwwQpvn1z208nDPbeiFhqGpcYTxdwZuFeQbx3A85Shke5cSZsT35JEHWBc7zFn4Ibt whbcBTPlXYZk+JQ0IbTt8BzAU7SLpAM8BLQ0piJQrYs2FT7c7kwKHBRxtvCggR22S/Os ToNBOf5X7zXI3Vd3I/zKmsH6MavzavFu3q2pyJV1DXQk5Mr3cQ7XG3N4IBT5bAIqTTH5 u78g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=eVprmkX04/ZA2Ox8rlDXhtYrH8Cdrulho+SeNeN/8to=; b=uCFgb1wq/Mix6yGb73UHN9Sz6IO31DZVLprEgOAaFJdB5LNVG57d/gSX/94Sqfs8HS TxiEttIU7LGIexp2gYff9eREo3wDkh2k0F6BetWcMt/+5nf6n9W+wy7FxZNzHh/W63wC LURgLz+gmRCK5+DrCLMCqNz8D6qFQUo8C3RuuLQAqUny3XU0zBv2DFXOrD+hC84MU5oh 8rkElrcd6FNoQ6RZEBvya0wc3joraz1w4iWYRYRnSko3+bhyg80abIg3bCVAzDEekeW2 Jt/hPSKBxrjVIp+EyQ/cXCALq63acU2+iUkHgdQWuzi4nh9gVQotNROz9JEdRYha0ast WS9g== X-Gm-Message-State: APjAAAUy9YecQ8Y917NrzyBSeIijPWp5mvyf1XFsZrBjQnbRKwhsegl2 BJjpIbjY7IRQsq+u4LB/fQHIIdEGyxHy9zA1/qznoA== X-Google-Smtp-Source: APXvYqwU6TvB7JcE/3RASUPFThxDiWpcs5rUTJFNuWlv+3cPwgOkF4im9S52I4IaK/gV84FJf6KuxUd7LyOYLmW+s08= X-Received: by 2002:a19:6b0e:: with SMTP id d14mr10053401lfa.151.1575971038660; Tue, 10 Dec 2019 01:43:58 -0800 (PST) MIME-Version: 1.0 References: <20191115045634.GN4614@dread.disaster.area> <20191115070843.GA24246@ming.t460p> <20191115234005.GO4614@dread.disaster.area> <20191118092121.GV4131@hirez.programming.kicks-ass.net> <20191118204054.GV4614@dread.disaster.area> <20191120191636.GI4097@hirez.programming.kicks-ass.net> <20191120220313.GC18056@pauld.bos.csb> <20191121132937.GW4114@hirez.programming.kicks-ass.net> <20191209165122.GA27229@linux.vnet.ibm.com> <20191209231743.GA19256@dread.disaster.area> <20191210054330.GF27253@linux.vnet.ibm.com> In-Reply-To: <20191210054330.GF27253@linux.vnet.ibm.com> From: Vincent Guittot Date: Tue, 10 Dec 2019 10:43:46 +0100 Message-ID: Subject: Re: [PATCH v2] sched/core: Preempt current task in favour of bound kthread To: Srikar Dronamraju Cc: Dave Chinner , Peter Zijlstra , Phil Auld , Ming Lei , linux-block , linux-fs , linux-xfs , linux-kernel , Jeff Moyer , Dave Chinner , Eric Sandeen , Christoph Hellwig , Jens Axboe , Ingo Molnar , Tejun Heo Content-Type: text/plain; charset="UTF-8" Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Tue, 10 Dec 2019 at 06:43, Srikar Dronamraju wrote: > > A running task can wake-up a per CPU bound kthread on the same CPU. > If the current running task doesn't yield the CPU before the next load > balance operation, the scheduler would detect load imbalance and try to > balance the load. However this load balance would fail as the waiting > task is CPU bound, while the running task cannot be moved by the regular > load balancer. Finally the active load balancer would kick in and move > the task to a different CPU/Core. Moving the task to a different > CPU/core can lead to loss in cache affinity leading to poor performance. > > This is more prone to happen if the current running task is CPU > intensive and the sched_wake_up_granularity is set to larger value. > When the sched_wake_up_granularity was relatively small, it was observed > that the bound thread would complete before the load balancer would have > chosen to move the cache hot task to a different CPU. > > To deal with this situation, the current running task would yield to a > per CPU bound kthread, provided kthread is not CPU intensive. > > /pboffline/hwcct_prg_old/lib/fsperf -t overwrite --noclean -f 5g -b 4k /pboffline > > (With sched_wake_up_granularity set to 15ms) So you increase sched_wake_up_granularity to a high level to ensure that current is no preempted by waking thread but then you add a way to finally preempt it which is somewhat weird IMO Have you tried to increase the priority of workqueue thread (decrease nice priority) ? This is the right way to reduce the impact of the sched_wake_up_granularity on the wakeup of your specific kthread. Because what you want at the end is keeping a low wakeup granularity for these io workqueues > > Performance counter stats for 'system wide' (5 runs): > event v5.4 v5.4 + patch(v2) > probe:active_load_balance_cpu_stop 1,919 ( +- 2.89% ) 5 ( +- 12.56% ) > sched:sched_waking 441,535 ( +- 0.17% ) 901,174 ( +- 0.25% ) > sched:sched_wakeup 441,533 ( +- 0.17% ) 901,172 ( +- 0.25% ) > sched:sched_wakeup_new 2,436 ( +- 8.08% ) 525 ( +- 2.57% ) > sched:sched_switch 797,007 ( +- 0.26% ) 1,458,463 ( +- 0.24% ) > sched:sched_migrate_task 20,998 ( +- 1.04% ) 2,279 ( +- 3.47% ) > sched:sched_process_free 2,436 ( +- 7.90% ) 527 ( +- 2.30% ) > sched:sched_process_exit 2,451 ( +- 7.85% ) 542 ( +- 2.24% ) > sched:sched_wait_task 7 ( +- 21.20% ) 1 ( +- 77.46% ) > sched:sched_process_wait 3,951 ( +- 9.14% ) 816 ( +- 3.52% ) > sched:sched_process_fork 2,435 ( +- 8.09% ) 524 ( +- 2.58% ) > sched:sched_process_exec 1,023 ( +- 12.21% ) 198 ( +- 3.23% ) > sched:sched_wake_idle_without_ipi 187,794 ( +- 1.14% ) 348,565 ( +- 0.34% ) > > Elasped time in seconds 289.43 +- 1.42 ( +- 0.49% ) 72.6013 +- 0.0417 ( +- 0.06% ) > Throughput results > > v5.4 > Trigger time:................... 0.842679 s (Throughput: 6075.86 MB/s) > Asynchronous submit time:....... 1.0184 s (Throughput: 5027.49 MB/s) > Synchronous submit time:........ 0 s (Throughput: 0 MB/s) > I/O time:....................... 263.17 s (Throughput: 19.455 MB/s) > Ratio trigger time to I/O time:.0.00320202 > > v5.4 + patch(v2) > Trigger time:................... 0.853973 s (Throughput: 5995.5 MB/s) > Asynchronous submit time:....... 0.768092 s (Throughput: 6665.86 MB/s) > Synchronous submit time:........ 0 s (Throughput: 0 MB/s) > I/O time:....................... 44.0267 s (Throughput: 116.292 MB/s) > Ratio trigger time to I/O time:.0.0193966 > > (With sched_wake_up_granularity set to 4ms) > > Performance counter stats for 'system wide' (5 runs): > event v5.4 v5.4 + patch(v2) > probe:active_load_balance_cpu_stop 6 ( +- 6.03% ) 5 ( +- 23.20% ) > sched:sched_waking 899,880 ( +- 0.38% ) 899,737 ( +- 0.41% ) > sched:sched_wakeup 899,878 ( +- 0.38% ) 899,736 ( +- 0.41% ) > sched:sched_wakeup_new 622 ( +- 11.95% ) 499 ( +- 1.08% ) > sched:sched_switch 1,458,214 ( +- 0.40% ) 1,451,374 ( +- 0.32% ) > sched:sched_migrate_task 3,120 ( +- 10.00% ) 2,500 ( +- 10.86% ) > sched:sched_process_free 608 ( +- 12.18% ) 484 ( +- 1.19% ) > sched:sched_process_exit 623 ( +- 11.91% ) 499 ( +- 1.15% ) > sched:sched_wait_task 1 ( +- 31.18% ) 1 ( +- 31.18% ) > sched:sched_process_wait 998 ( +- 13.22% ) 765 ( +- 0.16% ) > sched:sched_process_fork 622 ( +- 11.95% ) 498 ( +- 1.08% ) > sched:sched_process_exec 242 ( +- 13.81% ) 183 ( +- 0.48% ) > sched:sched_wake_idle_without_ipi 349,165 ( +- 0.35% ) 347,773 ( +- 0.43% ) > > Elasped time in seconds 72.8560 +- 0.0768 ( +- 0.11% ) 72.4327 +- 0.0797 ( +- 0.11% ) > > Signed-off-by: Srikar Dronamraju > --- > Changelog: > v1 : http://lore.kernel.org/lkml/20191209165122.GA27229@linux.vnet.ibm.com > v1->v2: Pass the the right params to try_to_wake_up as correctly pointed out > by Dave Chinner > > > kernel/sched/core.c | 7 ++++++- > kernel/sched/fair.c | 23 ++++++++++++++++++++++- > kernel/sched/sched.h | 3 ++- > 3 files changed, 30 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 44123b4d14e8..82126cbf62cd 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2664,7 +2664,12 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) > */ > int wake_up_process(struct task_struct *p) > { > - return try_to_wake_up(p, TASK_NORMAL, 0); > + int wake_flags = 0; > + > + if (is_per_cpu_kthread(p)) > + wake_flags = WF_KTHREAD; > + > + return try_to_wake_up(p, TASK_NORMAL, wake_flags); > } > EXPORT_SYMBOL(wake_up_process); > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 69a81a5709ff..36486f71e59f 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6660,6 +6660,27 @@ static void set_skip_buddy(struct sched_entity *se) > cfs_rq_of(se)->skip = se; > } > > +static int kthread_wakeup_preempt(struct rq *rq, struct task_struct *p, int wake_flags) > +{ > + struct task_struct *curr = rq->curr; > + struct cfs_rq *cfs_rq = task_cfs_rq(curr); > + > + if (!(wake_flags & WF_KTHREAD)) > + return 0; > + > + if (p->nr_cpus_allowed != 1 || curr->nr_cpus_allowed == 1) > + return 0; > + > + if (cfs_rq->nr_running > 2) > + return 0; > + > + /* > + * Don't preempt, if the waking kthread is more CPU intensive than > + * the current thread. > + */ > + return p->nvcsw * curr->nivcsw >= p->nivcsw * curr->nvcsw; > +} > + > /* > * Preempt the current task with a newly woken task if needed: > */ > @@ -6716,7 +6737,7 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_ > find_matching_se(&se, &pse); > update_curr(cfs_rq_of(se)); > BUG_ON(!pse); > - if (wakeup_preempt_entity(se, pse) == 1) { > + if (wakeup_preempt_entity(se, pse) == 1 || kthread_wakeup_preempt(rq, p, wake_flags)) { > /* > * Bias pick_next to pick the sched entity that is > * triggering this preemption. > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index c8870c5bd7df..23d4284ad1e3 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1643,7 +1643,8 @@ static inline int task_on_rq_migrating(struct task_struct *p) > */ > #define WF_SYNC 0x01 /* Waker goes to sleep after wakeup */ > #define WF_FORK 0x02 /* Child wakeup after fork */ > -#define WF_MIGRATED 0x4 /* Internal use, task got migrated */ > +#define WF_MIGRATED 0x04 /* Internal use, task got migrated */ > +#define WF_KTHREAD 0x08 /* Per CPU Kthread*/ > > /* > * To aid in avoiding the subversion of "niceness" due to uneven distribution > -- > 2.18.1 >