linux-kernel - Re: [PATCH 2/5] vmevent: Convert from deferred timer to deferred work

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Message-ID: <20120608080704.GB6362@lizard>
Date:	Fri, 8 Jun 2012 01:07:05 -0700
From:	Anton Vorontsov <anton.vorontsov@...aro.org>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Leonid Moiseichuk <leonid.moiseichuk@...ia.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	John Stultz <john.stultz@...aro.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linaro-kernel@...ts.linaro.org,
	patches@...aro.org, kernel-team@...roid.com
Subject: Re: [PATCH 2/5] vmevent: Convert from deferred timer to deferred work

On Fri, Jun 08, 2012 at 10:03:24AM +0300, Pekka Enberg wrote:
> On Fri, Jun 8, 2012 at 9:58 AM, Anton Vorontsov
> <anton.vorontsov@...aro.org> wrote:
> > If you're saying that we should set up a timer in the userland and
> > constantly read /proc/vmstat, then we will cause CPU wake up
> > every 100ms, which is not acceptable. Well, we can try to introduce
> > deferrable timers for the userspace. But then it would still add
> > a lot more overhead for our task, as this solution adds other two
> > context switches to read and parse /proc/vmstat. I guess this is
> > not a show-stopper though, so we can discuss this.
> >
> > Leonid, Pekka, what do you think about the idea?
> 
> That's exactly the kind of half-assed ABI that lead to people
> inventing out-of-tree lowmem notifiers in the first place.

:-)

Well, at least powersaving-wise, the solution w/ userland deferred
timers would be much better then just looping over /proc/vmstat each
100ms, and it is comparable to vmevent. Not pretty, but still would
work.

> I'd be more interested to know what people think of Minchan's that
> gets rid of vmstat sampling.

I answered to Minchan's post. The thing is that Minchan's idea
is not a substitution for vmevent. To me it seems like a shrinker w/
some pre-filter.

Thanks,

-- 
Anton Vorontsov
Email: cbouatmailru@...il.com
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