linux-kernel - Re: [RFC 0/2] drivers: spi/i2c: account completions as iowait

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sun, 2 Nov 2014 17:59:43 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Wolfram Sang <wsa@...-dreams.de>
Cc:	linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
	linux-spi@...r.kernel.org, Mark Brown <broonie@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Balbir Singh <bsingharora@...il.com>
Subject: Re: [RFC 0/2] drivers: spi/i2c: account completions as iowait

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.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/