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From: Vlastimil Babka <vbabka@suse.cz>
To: Christopher Lameter <cl@linux.com>,
	Marcelo Tosatti <mtosatti@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>,
	linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
	Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH] mm: introduce sysctl file to flush per-cpu vmstat statistics
Date: Tue, 24 Nov 2020 18:12:29 +0100	[thread overview]
Message-ID: <72f598ea-9fdf-537d-0b3a-aac2251d347c@suse.cz> (raw)
In-Reply-To: <alpine.DEB.2.22.394.2011201817320.248402@www.lameter.com>

On 11/20/20 7:20 PM, Christopher Lameter wrote:
> On Tue, 17 Nov 2020, Marcelo Tosatti wrote:
> 
>> > 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?
> 
> Yes. Introduce a sysctl to quiet down the system. Clean caches that will
> trigger kernel threads and whatever else is pending on that processor.

Please CC linux-api on future postings that introduce stuff like this.

>> 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.
> 
> There are typically pending actions that still trigger interruptions.
> 
> If you would immediately quiet down the system if there is only one thread
> runnable then you would compromise system performance through frequent
> counter folding and cache cleaning etc.

If someone goes through the trouble of setting up NOHZ, these 
disruptions should be only temporary and happen during the setup, no?


  parent reply	other threads:[~2020-11-24 17:15 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 [this message]
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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