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.
next prev 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 [PATCH] mm: introduce sysctl file to flush per-cpu vmstat statistics 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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