From: Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
To: Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>
Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
Balbir Singh
<bsingharora-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Subject: Re: [RFC 0/2] drivers: spi/i2c: account completions as iowait
Date: Sun, 2 Nov 2014 17:59:43 +0100 [thread overview]
Message-ID: <20141102165943.GT10501@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <1414936689-2707-1-git-send-email-wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>
On Sun, Nov 02, 2014 at 02:58:07PM +0100, Wolfram Sang wrote:
> However, researching the net, users currently interpret iowait entirely as
> blkio wait. Furthermore, io_schedule() calls delayacct_blkio_{start|end}() which
> worked fine for my tests with I2C but might show that iowait was really meant as
> blkiowait? So, should other subsystems use it?
I would tend to agree with that; historically this has always been about
blkio, not device io.
> To make it more confusing, some people (like Peter Zijlstra [1]) seem to like
> iowait gone, so maybe it is all not worth it?
Yeah, iowait accounting is terminally broken :-) Mostly because the
iowait is accounted per-cpu but that is a very tenuous relation because
the IO devices are not per IO and blocking tasks are not associated with
any particular CPU -- after all they're not consuming CPU time.
If people really think its worth; we could invent new IO-wait measure
that do make sense -- maybe, but the current thing is complete bollocks.
WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Wolfram Sang <wsa@the-dreams.de>
Cc: linux-kernel@vger.kernel.org, linux-i2c@vger.kernel.org,
linux-spi@vger.kernel.org, Mark Brown <broonie@kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Balbir Singh <bsingharora@gmail.com>
Subject: Re: [RFC 0/2] drivers: spi/i2c: account completions as iowait
Date: Sun, 2 Nov 2014 17:59:43 +0100 [thread overview]
Message-ID: <20141102165943.GT10501@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <1414936689-2707-1-git-send-email-wsa@the-dreams.de>
On Sun, Nov 02, 2014 at 02:58:07PM +0100, Wolfram Sang wrote:
> However, researching the net, users currently interpret iowait entirely as
> blkio wait. Furthermore, io_schedule() calls delayacct_blkio_{start|end}() which
> worked fine for my tests with I2C but might show that iowait was really meant as
> blkiowait? So, should other subsystems use it?
I would tend to agree with that; historically this has always been about
blkio, not device io.
> To make it more confusing, some people (like Peter Zijlstra [1]) seem to like
> iowait gone, so maybe it is all not worth it?
Yeah, iowait accounting is terminally broken :-) Mostly because the
iowait is accounted per-cpu but that is a very tenuous relation because
the IO devices are not per IO and blocking tasks are not associated with
any particular CPU -- after all they're not consuming CPU time.
If people really think its worth; we could invent new IO-wait measure
that do make sense -- maybe, but the current thing is complete bollocks.
next prev parent reply other threads:[~2014-11-02 16:59 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-02 13:58 [RFC 0/2] drivers: spi/i2c: account completions as iowait Wolfram Sang
2014-11-02 13:58 ` Wolfram Sang
2014-11-02 13:58 ` [RFC 1/2] i2c: " Wolfram Sang
[not found] ` <1414936689-2707-1-git-send-email-wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>
2014-11-02 13:58 ` [RFC 2/2] spi: " Wolfram Sang
2014-11-02 13:58 ` Wolfram Sang
2014-11-02 16:59 ` Peter Zijlstra [this message]
2014-11-02 16:59 ` [RFC 0/2] drivers: spi/i2c: " Peter Zijlstra
[not found] ` <20141102165943.GT10501-IIpfhp3q70z/8w/KjCw3T+5/BudmfyzbbVWyRVo5IupeoWH0uzbU5w@public.gmane.org>
2014-11-03 19:31 ` Wolfram Sang
2014-11-03 19:31 ` Wolfram Sang
2014-11-03 13:02 ` One Thousand Gnomes
[not found] ` <20141103130222.1c53fa39-mUKnrFFms3BCCTY1wZZT65JpZx93mCW/@public.gmane.org>
2014-11-03 19:45 ` Wolfram Sang
2014-11-03 19:45 ` Wolfram Sang
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