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

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Message-ID: <CA+55aFx43+qb-Mz+P_gcJjNMD4=Qi0Q14LKCR1macppWy2xJxQ@mail.gmail.com>
Date:	Fri, 13 Apr 2012 11:33:10 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	Andi Kleen <andi@...stfloor.org>, "Ted Ts'o" <tytso@....edu>,
	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 11:31 AM, Tim Chen <tim.c.chen@...ux.intel.com> wrote:
>
> Benchmark is working on files on normal hard disk.
> However, I have I have a large number
> of processes (80 processes, one for each cpu), each reading
> a separate mmaped file.  The files are in the same directory.
> That makes cache line bouncing on the counters particularly bad
> due to the large number of processes running.

Ok, that sounds like a potentially realistic case then, even if your
benchmark probably shows the worst possible case.

Considering that the counters are apparently not all that useful, it
does sound like they should just be removed, Ted.

                          Linus
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