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From: Andrei Vagin <avagin@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org,
	Andy Lutomirski <luto@amacapital.net>,
	Christian Brauner <brauner@kernel.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Kees Cook <keescook@chromium.org>, Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Peter Oskolkov <posk@google.com>,
	Tycho Andersen <tycho@tycho.pizza>,
	Will Drewry <wad@chromium.org>,
	Vincent Guittot <vincent.guittot@linaro.org>
Subject: Re: [PATCH 3/5] sched: add a few helpers to wake up tasks on the current cpu
Date: Thu, 20 Oct 2022 17:44:51 -0700	[thread overview]
Message-ID: <Y1Hrg/sqPhuSr+PY@gmail.com> (raw)
In-Reply-To: <Y1FX6FmPHCsdQn9A@hirez.programming.kicks-ass.net>

On Thu, Oct 20, 2022 at 04:15:04PM +0200, Peter Zijlstra wrote:
> On Wed, Oct 19, 2022 at 06:10:46PM -0700, Andrei Vagin wrote:
> > Add complete_on_current_cpu, wake_up_poll_on_current_cpu helpers to wake
> > up processes on the current CPU.
>
> There is an astounding lack of *why* in this changelog.

I use them in the next patch to handle seccomp user notify requests
faster.

The seccomp notify mechanism allows less privileged processes to offload
specific syscalls to more privileged processes.  In many cases, the
workflow is fully synchronous. It means a target process triggers a
system call, the kernel stops it and wakes up a supervisor process that
handles the system call and returns controls back to the target process.
In this context, "synchronous" means that only one process is running
and another one is waiting.

New helpers advices the scheduler to move the wakee to the current CPU.
For synchronous workflows like described above, these helpers makes
context switches a few times faster.

For example, using these helpers allows to reduce a seccomp user notify
rountdrip time from 12µs to 3µs.

Thanks,
Andrei

  reply	other threads:[~2022-10-21  0:45 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
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 1/5] seccomp: don't use semaphore and wait_queue together Andrei Vagin
2022-10-20  5:10   ` Kees Cook
2022-10-21  4:30     ` 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
2022-10-20  1:10 ` [PATCH 3/5] sched: add a few helpers to wake up tasks on the current cpu Andrei Vagin
2022-10-20 14:15   ` Peter Zijlstra
2022-10-21  0:44     ` Andrei Vagin [this message]
2022-10-27  6:51       ` Andrei Vagin
2022-10-20  1:10 ` [PATCH 4/5] seccomp: add the synchronous mode for seccomp_unotify Andrei Vagin
2022-10-20  1:10 ` [PATCH 5/5] selftest/seccomp: add a new test for the sync mode of seccomp_user_notify Andrei Vagin
2022-10-20  5:04   ` Kees Cook
2022-10-21  0:53     ` Andrei Vagin
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 3/5] sched: add a few helpers to wake up tasks on the current cpu Andrei Vagin
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 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

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