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From: Waiman Long <longman@redhat.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Kees Cook <keescook@chromium.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	Davidlohr Bueso <dave@stgolabs.net>,
	Miklos Szeredi <miklos@szeredi.hu>,
	Daniel Colascione <dancol@google.com>,
	Dave Chinner <david@fromorbit.com>,
	Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [PATCH v2 0/4] /proc/stat: Reduce irqs counting performance overhead
Date: Wed, 9 Jan 2019 13:03:33 -0500	[thread overview]
Message-ID: <f6302369-9eda-ef58-4f18-3dc9ffbc31f1@redhat.com> (raw)
In-Reply-To: <20190109174403.GN6310@bombadil.infradead.org>

On 01/09/2019 12:44 PM, Matthew Wilcox wrote:
> On Wed, Jan 09, 2019 at 12:23:44PM -0500, Waiman Long wrote:
>> This v2 patch optimizes the way the IRQ counts are retrieved and computed
>> and getting rid of the sysctl parameter altogether to achieve a performance
>> gain that is close to the v1 patch. This is based on the idea that while
>> many IRQs can be supported by a system, only a handful of them are actually
>> being used in most cases. We can save a lot of time by focusing on those
>> active IRQs only and ignore the rests.
> So your reaction to being told "Make this the same as every other thing
> we have to sum across all CPUs" is to make it _even more different_ and
> special-cased?  I'm done.  NAK.

The paragraph above may be a bit misleading. This v2 patch actually
touches very little on percpu accounting aspect of the IRQ counts. See
patches 2 and 3 for the relevant changes which is just a few line of new
codes. Please review the individual patches before Nak'ing.

I could theoretically generalize them into a new set of percpu counting
helpers, but the idea behind it is quite different from the use cases of
percpu counter. So it may not be a good idea of adding it to there.

Cheers,
Longman

  reply	other threads:[~2019-01-09 18:03 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-09 17:23 [PATCH v2 0/4] /proc/stat: Reduce irqs counting performance overhead Waiman Long
2019-01-09 17:23 ` [PATCH v2 1/4] /proc/stat: Extract irqs counting code into show_stat_irqs() Waiman Long
2019-01-09 17:23 ` [PATCH v2 2/4] /proc/stat: Only do percpu sum of active IRQs Waiman Long
2019-01-09 17:23 ` [PATCH v2 3/4] genirq: Track the number " Waiman Long
2019-01-09 17:23 ` [PATCH v2 4/4] /proc/stat: Call kstat_irqs_usr() only for " Waiman Long
2019-01-09 17:23   ` Waiman Long
2019-01-09 17:39   ` Waiman Long
2019-01-09 17:44 ` [PATCH v2 0/4] /proc/stat: Reduce irqs counting performance overhead Matthew Wilcox
2019-01-09 18:03   ` Waiman Long [this message]
2019-01-09 18:24     ` Matthew Wilcox
2019-01-09 18:37       ` Waiman Long
2019-01-09 18:52         ` Matthew Wilcox
2019-01-09 18:57           ` Waiman Long
2019-01-09 18:54         ` Waiman Long
2019-01-09 19:59           ` Matthew Wilcox
2019-01-09 19:59             ` Matthew Wilcox
2019-01-09 20:14             ` Waiman Long
2019-01-09 20:14               ` Waiman Long

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