linux-kernel - Re: [patch 1/4] x86: FIFO ticket spinlocks

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Message-ID: <20071101203526.293cd7f0@bree.surriel.com>
Date:	Thu, 1 Nov 2007 20:35:26 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Gregory Haskins <gregory.haskins.ml@...il.com>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...e.de>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch 1/4] x86: FIFO ticket spinlocks

On Thu, 1 Nov 2007 09:38:22 -0700 (PDT)
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> So "unfair" is obviously always bad. Except when it isn't.

Larry Woodman managed to wedge the VM into a state where, on his
4x dual core system, only 2 cores (on the same CPU) could get the
zone->lru_lock overnight.  The other 6 cores on the system were
just spinning, without being able to get the lock.

On the other hand, spinlock contention in the page replacement
code is just a symptom of the fact that we scan too many pages.
It can probably be fixed in other ways...

-- 
"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it." - Brian W. Kernighan
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