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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/
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