From: Marcelo Tosatti <email@example.com> To: Christopher Lameter <firstname.lastname@example.org> Cc: Matthew Wilcox <email@example.com>, firstname.lastname@example.org, Andrew Morton <email@example.com> Subject: Re: [PATCH] mm: introduce sysctl file to flush per-cpu vmstat statistics Date: Mon, 23 Nov 2020 15:02:23 -0300 [thread overview] Message-ID: <20201123180223.GA19269@fuller.cnet> (raw) In-Reply-To: <alpine.DEB.firstname.lastname@example.org> On Fri, Nov 20, 2020 at 06:20:06PM +0000, 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. OK, makes sense. About sysctl, in particular: NOTES top Use of this system call was long discouraged: since Linux 2.6.24, uses of this system call result in warnings in the kernel log, and in Linux 5.5, the system call was finally removed. Use the /proc/sys interface instead. Note that on older kernels where this system call still exists, it is available only if the kernel was configured with the CONFIG_SYSCTL_SYSCALL option. Furthermore, glibc does not provide a wrapper for this system call, necessitating the use of syscall(2). So will stick to the /proc/ suggestion. > > 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. Makes sense.
next prev parent reply other threads:[~2020-11-24 18:29 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 [this message] 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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