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From: Christoph Lameter <cl@linux.com>
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>,
	linux-mm@kvack.org,  Andrew Morton <akpm@linux-foundation.org>,
	 Alex Belits <abelits@marvell.com>, Phil Auld <pauld@redhat.com>,
	 Thomas Gleixner <tglx@linutronix.de>,
	 Frederic Weisbecker <frederic@kernel.org>,
	 Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH] mm: introduce sysctl file to flush per-cpu vmstat statistics
Date: Mon, 30 Nov 2020 09:31:47 +0000 (UTC)	[thread overview]
Message-ID: <alpine.DEB.2.22.394.2011300927120.337729@www.lameter.com> (raw)
In-Reply-To: <20201127154845.GA9100@fuller.cnet>

On Fri, 27 Nov 2020, Marcelo Tosatti wrote:

> Decided to switch to prctl interface, and then it starts
> to become similar to "task mode isolation" patchset API.

Right I think that was a good approach.

> In addition to quiescing pending activities on the CPU, it would
> also be useful to assign a per-task attribute (which is then assigned
> to a per-CPU attribute), indicating whether that CPU is running
> an isolated task or not.

Sounds good but what would this do? Give a warning like the isolation
patchset?

> This per-CPU attribute can be used to, for example, return -EBUSY
> from ring_buffer_resize() (or any other IPI generating activity
> which can return an error to userspace).

Yes good.

> So rather than:
>
> 	prctl(PR_QUIESCE_CPU)	(current interface, similar to
> 	initial message on the thread but with prctl rather than
> 	sysfs)
>
> To be called before real time loop, one would have:
>
> 	prctl(PR_SET_TASK_ISOLATION, ISOLATION_ENABLE) [1]
> 	real time loop
> 	prctl(PR_SET_TASK_ISOLATION, ISOLATION_DISABLE)
>
> (with the attribute also being cleared on task exit).
>
> The general description would be:
>
> "Set task isolated mode for a given task, returning an error
> if the task is not pinned to a single CPU.
>
> In this mode, the kernel will avoid interruptions to isolated
> CPUs when possible."
>
> Any objections against such an interface ?

Maybe do both like in the isolation patchset?

Often code can tolerate a few interruptions (in some code branches
regular syscalls may be needed) but one wants the thread to be
as quiet as possible.





  parent reply	other threads:[~2020-11-30  9:32 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-17 16:28 Marcelo Tosatti
2020-11-17 18:03 ` Matthew Wilcox
2020-11-17 19:06   ` Christopher Lameter
2020-11-17 19:09     ` Matthew Wilcox
2020-11-20 18:04       ` Christopher Lameter
2020-11-17 20:23     ` Marcelo Tosatti
2020-11-20 18:02       ` Marcelo Tosatti
2020-11-20 18:20       ` Christopher Lameter
2020-11-23 18:02         ` Marcelo Tosatti
2020-11-24 17:12         ` Vlastimil Babka
2020-11-24 19:52           ` Marcelo Tosatti
2020-11-27 15:48         ` Marcelo Tosatti
2020-11-28  3:49           ` [EXT] " Alex Belits
2020-11-30 18:18             ` Marcelo Tosatti
2020-11-30 18:29               ` Marcelo Tosatti
2020-12-03 22:47                 ` Alex Belits
2020-12-03 22:21               ` Alex Belits
2020-11-30  9:31           ` Christoph Lameter [this message]
2020-12-02 12:43             ` Marcelo Tosatti
2020-12-02 15:57             ` Thomas Gleixner
2020-12-02 17:43               ` Christoph Lameter
2020-12-03  3:17                 ` Thomas Gleixner
2020-12-07  8:08                   ` Christoph Lameter
2020-12-07 16:09                     ` Thomas Gleixner
2020-12-07 19:01                       ` Thomas Gleixner
2020-12-02 18:38               ` Marcelo Tosatti
2020-12-04  0:20                 ` Frederic Weisbecker
2020-12-04 13:31                   ` Marcelo Tosatti
2020-12-04  1:43               ` [EXT] " Alex Belits
2021-01-13 12:15                 ` [RFC] tentative prctl task isolation interface Marcelo Tosatti
2021-01-14  9:22                   ` Christoph Lameter
2021-01-14 19:34                     ` Marcelo Tosatti
2021-01-15 13:24                       ` Christoph Lameter
2021-01-15 18:35                         ` Alex Belits
2021-01-21 15:51                           ` Marcelo Tosatti
2021-01-21 16:20                             ` Marcelo Tosatti
2021-01-22 13:05                               ` Marcelo Tosatti
2021-02-01 10:48                             ` Christoph Lameter
2021-02-01 12:47                               ` Alex Belits
2021-02-01 18:20                               ` Marcelo Tosatti
2021-01-18 15:18                         ` Marcelo Tosatti
2020-11-24  5:02 ` [mm] e655d17ffa: BUG:using_smp_processor_id()in_preemptible kernel test robot

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