From: Dave Chinner <david@fromorbit.com>
To: Waiman Long <longman@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Alexey Dobriyan <adobriyan@gmail.com>,
Luis Chamberlain <mcgrof@kernel.org>,
Kees Cook <keescook@chromium.org>,
Jonathan Corbet <corbet@lwn.net>,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
linux-fsdevel@vger.kernel.org,
Davidlohr Bueso <dave@stgolabs.net>,
Miklos Szeredi <miklos@szeredi.hu>,
Daniel Colascione <dancol@google.com>,
Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [PATCH 0/2] /proc/stat: Reduce irqs counting performance overhead
Date: Tue, 8 Jan 2019 09:32:14 +1100 [thread overview]
Message-ID: <20190107223214.GZ6311@dastard> (raw)
In-Reply-To: <1546873978-27797-1-git-send-email-longman@redhat.com>
On Mon, Jan 07, 2019 at 10:12:56AM -0500, Waiman Long wrote:
> As newer systems have more and more IRQs and CPUs available in their
> system, the performance of reading /proc/stat frequently is getting
> worse and worse.
Because the "roll-your-own" per-cpu counter implementaiton has been
optimised for low possible addition overhead on the premise that
summing the counters is rare and isn't a performance issue. This
patchset is a direct indication that this "summing is rare and can
be slow" premise is now invalid.
We have percpu counter infrastructure that trades off a small amount
of addition overhead for zero-cost reading of the counter value.
i.e. why not just convert this whole mess to percpu_counters and
then just use percpu_counter_read_positive()? Then we just don't
care how often userspace reads the /proc file because there is no
summing involved at all...
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2019-01-07 22:32 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-07 15:12 [PATCH 0/2] /proc/stat: Reduce irqs counting performance overhead Waiman Long
2019-01-07 15:12 ` [PATCH 1/2] /proc/stat: Extract irqs counting code into show_stat_irqs() Waiman Long
2019-01-07 21:42 ` Kees Cook
2019-01-07 15:12 ` [PATCH 2/2] /proc/stat: Add sysctl parameter to control irq counts latency Waiman Long
2019-01-07 15:58 ` Matthew Wilcox
2019-01-07 16:07 ` Waiman Long
2019-01-07 16:14 ` Matthew Wilcox
2019-01-07 16:19 ` Waiman Long
2019-01-07 16:33 ` Alexey Dobriyan
2019-01-07 16:59 ` Waiman Long
[not found] ` <20190118084456.GA10690@shao2-debian>
2019-01-21 20:02 ` [LKP] [/proc/stat] 3047027b34: reaim.jobs_per_min -4.8% regression Kees Cook
2019-01-21 21:25 ` Alexey Dobriyan
2019-01-07 22:32 ` Dave Chinner [this message]
2019-01-07 22:41 ` [PATCH 0/2] /proc/stat: Reduce irqs counting performance overhead Daniel Colascione
2019-01-07 23:49 ` Alexey Dobriyan
2019-01-07 22:41 ` Waiman Long
2019-01-08 2:04 ` Dave Chinner
2019-01-08 16:11 ` Michal Hocko
2019-01-08 17:05 ` Waiman Long
2019-01-08 17:32 ` Waiman Long
2019-01-08 16:58 ` Waiman Long
2019-01-08 22:27 ` Dave Chinner
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