linux-ext4 - Re: spinlocks in ext4

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Message-ID: <CAK5=ZRJt3KCQniUA+-E4kn_51nFvB34796wOoG4vrmzU5nfwOA@mail.gmail.com>
Date:	Thu, 11 Oct 2012 11:37:46 -0700
From:	Peter Fordham <peter.fordham@...il.com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: spinlocks in ext4

On 8 October 2012 18:10, Theodore Ts'o <tytso@....edu> wrote:
> How expensive are memory barriers on ARM, anyway?

The performance monitors seem to be telling me that a DMB just after a
store which misses in the L1 & L2, (causing an eviction of a clean
line and a line-fill, I assume) takes over 100 cycles.

I'm seeing a 20% slow down in ext4 performance when enabling SMP on my
device. I'm starting to think there might be issues with the memory
system.

-Pete
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