linux-kernel - Re: Poor desktop responsiveness with background I/O-operations

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Message-ID: <m3tyyw6pvz.fsf@lugabout.jhcloos.org>
Date:	Mon, 21 Sep 2009 15:47:36 -0400
From:	James Cloos <cloos@...loos.com>
To:	lkml <linux-kernel@...r.kernel.org>
Cc:	Ulrich Lukas <stellplatz-nr.13a@...enparkplatz.de>,
	Mike Galbraith <efault@....de>
Subject: Re: Poor desktop responsiveness with background I/O-operations

FWIW, I did not notice any problems with the last kernel I had compiled
in the -- IIRC -- 29-rc timeframe.  Or maybe it was the 30-rc timeframe.

I had that kernel up for soemthing like five weeks, on a busy, low-ram
laptop, w/o and long pauses or other noticeable pain.  For at least two
years before that the best this laptop could manage before latency
became horrific was a fortnight, and weekly reboots were desirable.

Unfortunately, before I could send out a congratulatory note (I wanted
to first confirm that the result remained) I pulled up and started see-
ing even worse latency then ever.

Turning ext4 barriers off helped avoid some of the new latency, and my
current compile (master as of the 17th) is much better than .31 was.

But long pauses still occur whenever paging and backgound i/o-bound
tasks interact.

There was a major regression in paging performance either .30 or .31
(see above).  Interestingly, top(1) also shows less swap usage for
the same usage patterns than with the older kernels.  I don't know
which is cause or which is effect.

A git pull on a clone of Linus' tree is a great way to trigger the
problem.  As is using Gentoo's portage to install/upgrade anything.
(Bad python; no alligator!¹)  (Yes, that is a burlesque of the no
doughnut joke.)

[1] Pythons which have invaded Florida have reportedly been
    witnessed eating alligators, according to a recent wire
    service article.

-JimC
-- 
James Cloos <cloos@...loos.com>         OpenPGP: 1024D/ED7DAEA6
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