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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>,
	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>,
	Dave Chinner <david@fromorbit.com>,
	Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [PATCH 2/2] /proc/stat: Add sysctl parameter to control irq counts latency
Date: Mon, 7 Jan 2019 11:19:14 -0500	[thread overview]
Message-ID: <f8eefa83-f85e-0ba8-dcb9-a76a12449228@redhat.com> (raw)
In-Reply-To: <20190107161442.GZ6310@bombadil.infradead.org>

On 01/07/2019 11:14 AM, Matthew Wilcox wrote:
> On Mon, Jan 07, 2019 at 11:07:47AM -0500, Waiman Long wrote:
>>> Why are you caching the _output_ of calling sprintf(), rather than caching the
>>> values of each interrupt?
>>>
>> It is just faster to dump the whole string buffer than redoing the
>> number formatting each time when the values don't change. I can cache
>> the individual sums instead if it is the preferred by most.
> But it also consumes more memory.  Can you gather some measurements to
> find out what the performance difference is if you cache the values
> instead of the strings?

I allocate 11 bytes (10 digits + space) for each unsigned int IRQ value.
I needs 4 bytes for the unsigned value itself. So it is a saving of 7
bytes. With 4k irqs, it will be 28k.

I will run some measurements of caching the values versus saving the
string later this week.

Thanks,
Longman

  reply	other threads:[~2019-01-07 16:19 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 [this message]
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 ` [PATCH 0/2] /proc/stat: Reduce irqs counting performance overhead Dave Chinner
2019-01-07 22:41   ` 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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