From: Chen Yu <yu.c.chen@intel.com>
To: Andrei Vagin <avagin@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
<linux-kernel@vger.kernel.org>, Kees Cook <keescook@chromium.org>,
Christian Brauner <brauner@kernel.org>,
Andrei Vagin <avagin@gmail.com>,
Andy Lutomirski <luto@amacapital.net>,
Juri Lelli <juri.lelli@redhat.com>,
Peter Oskolkov <posk@google.com>,
Tycho Andersen <tycho@tycho.pizza>,
Will Drewry <wad@chromium.org>
Subject: Re: [PATCH 2/5] sched: add WF_CURRENT_CPU and externise ttwu
Date: Thu, 12 Jan 2023 15:35:39 +0800 [thread overview]
Message-ID: <Y7+4S9umCo5I+Ty7@chenyu5-mobl1> (raw)
In-Reply-To: <20230110213010.2683185-3-avagin@google.com>
On 2023-01-10 at 13:30:07 -0800, Andrei Vagin wrote:
> From: Peter Oskolkov <posk@google.com>
>
> Add WF_CURRENT_CPU wake flag that advices the scheduler to
> move the wakee to the current CPU. This is useful for fast on-CPU
> context switching use cases.
>
> In addition, make ttwu external rather than static so that
> the flag could be passed to it from outside of sched/core.c.
>
> Signed-off-by: Peter Oskolkov <posk@google.com>
> Signed-off-by: Andrei Vagin <avagin@gmail.com>
> @@ -7380,6 +7380,10 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags)
> if (wake_flags & WF_TTWU) {
> record_wakee(p);
>
> + if ((wake_flags & WF_CURRENT_CPU) &&
> + cpumask_test_cpu(cpu, p->cpus_ptr))
> + return cpu;
I agree that cross-CPU wake up brings pain to fast context switching
use cases, especially on high core count system. We suffered from this
issue as well, so previously we presented this issue as well. The difference
is that we used some dynamic "WF_CURRENT_CPU" mechanism[1] to deal with it.
That is, if the waker/wakee are both short duration tasks, let the waker wakes up
the wakee on current CPU. So not only seccomp but also other components/workloads
could benefit from this without having to set the WF_CURRENT_CPU flag.
Link [1]:
https://lore.kernel.org/lkml/cover.1671158588.git.yu.c.chen@intel.com/
thanks,
Chenyu
next prev parent reply other threads:[~2023-01-12 7:36 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-10 21:30 [PATCH 0/5 v3 RESEND] seccomp: add the synchronous mode for seccomp_unotify Andrei Vagin
2023-01-10 21:30 ` [PATCH 1/5] seccomp: don't use semaphore and wait_queue together Andrei Vagin
2023-01-12 14:58 ` Tycho Andersen
2023-01-13 21:51 ` Andrei Vagin
2023-01-16 9:48 ` Peter Zijlstra
2023-01-10 21:30 ` [PATCH 2/5] sched: add WF_CURRENT_CPU and externise ttwu Andrei Vagin
2023-01-12 7:35 ` Chen Yu [this message]
2023-01-13 21:39 ` Andrei Vagin
2023-01-14 15:59 ` Chen Yu
2023-01-18 6:10 ` Andrei Vagin
2023-01-10 21:30 ` [PATCH 3/5] sched: add a few helpers to wake up tasks on the current cpu Andrei Vagin
2023-01-16 9:59 ` Peter Zijlstra
2023-01-19 6:45 ` Andrei Vagin
2023-01-19 10:09 ` Peter Zijlstra
2023-01-10 21:30 ` [PATCH 4/5] seccomp: add the synchronous mode for seccomp_unotify Andrei Vagin
2023-01-12 15:00 ` Tycho Andersen
2023-01-14 1:16 ` Andrei Vagin
2023-01-10 21:30 ` [PATCH 5/5] selftest/seccomp: add a new test for the sync mode of seccomp_user_notify Andrei Vagin
-- strict thread matches above, loose matches on Subject: below --
2022-11-11 7:31 [PATCH 0/5 v3] seccomp: add the synchronous mode for seccomp_unotify Andrei Vagin
2022-11-11 7:31 ` [PATCH 2/5] sched: add WF_CURRENT_CPU and externise ttwu Andrei Vagin
2022-10-20 1:10 [PATCH 0/5 v2] seccomp: add the synchronous mode for seccomp_unotify Andrei Vagin
2022-10-20 1:10 ` [PATCH 2/5] sched: add WF_CURRENT_CPU and externise ttwu Andrei Vagin
2022-10-20 4:54 ` Kees Cook
2022-10-21 0:48 ` Andrei Vagin
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