Message-Id: <5.2.1.1.2.20051226175652.00be31b8@pop.gmx.net>
Date: Mon, 26 Dec 2005 18:15:17 +0100
To: Andrew Morton <akpm@osdl.org>, Arjan van de Ven <arjan@infradead.org>
From: Mike Galbraith <efault@gmx.de>
Subject: Re: [patch 0/9] mutex subsystem, -V4
Cc: mingo@elte.hu, zippel@linux-m68k.org, hch@infradead.org,
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       rmk+lkml@arm.linux.org.uk
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At 03:11 AM 12/26/2005 -0800, Andrew Morton wrote:
>Arjan van de Ven <arjan@infradead.org> wrote:
> >
> >
> > > hm.  16 CPUs hitting the same semaphore at great arrival rates.  The cost
> > > of a short spin is much less than the cost of a sleep/wakeup.  The 
> machine
> > > was doing 100,000 - 200,000 context switches per second.
> >
> > interesting.. this might be a good indication that a "spin a bit first"
> > mutex slowpath for some locks might be worth implementing...
>
>If we see a workload which is triggering such high context switch rates,
>maybe.  But I don't think we've seen any such for a long time.

Hmm.  Is there a real workload where such a high context switch rate is 
necessary?  Every time I've seen a high (100,000 - 200,000 is beyond absurd 
on my little box, but...) context switch rate, it's been because something 
sucked.

         -Mike   

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