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Date: Sun, 01 Sep 2002 15:09:36 -0700
From: Andrew Morton <akpm@zip.com.au>
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To: Daniel Phillips <phillips@arcor.de>
CC: Christian Ehrhardt <ehrhardt@mathematik.uni-ulm.de>,
       Linus Torvalds <torvalds@transmeta.com>,
       Marcelo Tosatti <marcelo@conectiva.com.br>,
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Subject: Re: [RFC] [PATCH] Include LRU in page count
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Daniel Phillips wrote:
> 
> ...
> I'm looking at your spinlock_irq now and thinking the _irq part could
> possibly be avoided.  Can you please remind me of the motivation for this -
> was it originally intended to address the same race we've been working on
> here?
> 

scalability, mainly.  If the CPU holding the lock takes an interrupt,
all the other CPUs get to spin until the handler completes.  I measured
a 30% reducton in contention from this.

Not a generally justifiable trick, but this is a heavily-used lock.
All the new games in refill_inactive() are there to minimise the
interrupt-off time.
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