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From: Marcelo Tosatti <mtosatti@redhat.com>
To: Christopher Lameter <cl@linux.com>
Cc: Matthew Wilcox <willy@infradead.org>,
	linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm: introduce sysctl file to flush per-cpu vmstat statistics
Date: Tue, 17 Nov 2020 17:23:17 -0300	[thread overview]
Message-ID: <20201117202317.GA282679@fuller.cnet> (raw)
In-Reply-To: <alpine.DEB.2.22.394.2011171855500.215602@www.lameter.com>

On Tue, Nov 17, 2020 at 07:06:33PM +0000, Christopher Lameter wrote:
> On Tue, 17 Nov 2020, Matthew Wilcox wrote:
> 
> > On Tue, Nov 17, 2020 at 01:28:06PM -0300, Marcelo Tosatti wrote:
> > > For isolated applications that busy loop (packet processing with DPDK,
> > > for example), workqueue functions either stall (if the -rt app priority
> > > is higher than kworker thread priority) or interrupt the -rt app
> > > (if the -rt app priority is lower than kworker thread priority.
> >
> > This seems a bit obscure to expect an application to do.  Can we make
> > this happen automatically when we bind an rt task to a group of CPUs?
>
> Well the way we used it was just to let things be and run in the busy
> loop. There could be another flush of the vmstat data and then the vmstat
> worker will disable itself. So two more workqueue executions before the
> processor completely dies down. But then we also need a period like
> that to trigger the NOHZ logic to switch off the timer. Right?

The application should not start its time sensitive loop until the
workqueues have finished execution.

> So what we would need would be something like a sysctl that puts the
> system into a quiet state by completing all workqueue items. Idle all
> subsystems that need it and put the cpu into NOHZ mode.

Are you suggesting that instead of a specific file to control vmstat 
workqueue only, a more generic sysctl could be used?

About NOHZ mode: the CPU should enter NOHZ automatically as soon as
there is a single thread running, so unclear why that would be needed.

Thanks.



  parent reply	other threads:[~2020-11-17 20:23 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 [this message]
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
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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