Messages in this thread | | | Subject | Re: [patch 0/9] mutex subsystem, -V4 | From | Lee Revell <> | Date | Mon, 26 Dec 2005 12:44:52 -0500 |
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On Mon, 2005-12-26 at 18:15 +0100, Mike Galbraith wrote: > 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.
I can trivially produce 20K per second on my little sub Ghz box so 100K on a busy server is certainly plausible. Especially if for the purposes of this discussion we are also worried about -rt + IRQ threading where each IRQ costs two context switches (more if it raises a softirq).
Lee
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