linux-ext4 - Re: [RFC, PATCH] Avoid hot statistics cache line in ext4 extent cache

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Message-ID: <20120413184823.GA5898@thunk.org>
Date:	Fri, 13 Apr 2012 14:48:23 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Tim Chen <tim.c.chen@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Vivek Haldar <haldar@...gle.com>,
	Andreas Dilger <adilger@...ger.ca>, linux-ext4@...r.kernel.org
Subject: Re: [RFC, PATCH] Avoid hot statistics cache line in ext4 extent
 cache

On Fri, Apr 13, 2012 at 08:41:58PM +0200, Andi Kleen wrote:
> > The reason why I ask this is we're seeing anything like this with Eric
> > Whitney's 48 CPU scalability testing; we're not CPU bottlenecked, and
> > I don't even see evidence of a larger than usual CPU utilization
> > compared to other file systems.
> 
> I bet Eric didn't test with this statistic counter.

Huh?  You can't turn it off, and he's been doing regular scalability
tests at least once per kernel release.

Can you say a bit more about exactly how you are doing this test and
what are the "other issues" where this is becoming a bottleneck?  If
possible I'd like to ask Eric if he can add it to his regular
scalability tests.

Thanks,

						 - Ted
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