Messages in this thread |  | | Date | Thu, 4 Oct 2001 16:50:13 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: Context switch times |
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On Thu, 4 Oct 2001, Mike Kravetz wrote:
> On Thu, Oct 04, 2001 at 10:42:37PM +0000, Linus Torvalds wrote: > > Could we try to hit just two? Probably, but it doesn't really matter, > > though: to make the lmbench scheduler benchmark go at full speed, you > > want to limit it to _one_ CPU, which is not sensible in real-life > > situations. > > Can you clarify? I agree that tuning the system for the best LMbench > performance is not a good thing to do! However, in general on an > 8 CPU system with only 2 'active' tasks I would think limiting the > tasks to 2 CPUs would be desirable for cache effects.
Yes, limiting to 2 CPU's probably gets better cache behaviour, and it might be worth looking into why it doesn't. The CPU affinity _should_ prioritize it down to two, but I haven't thought through your theory about IPI latency.
However, the reason 2.2.x does so well is that in 2.2.x it will stay on _once_ CPU if I remember correctly. We basically tuned the scheduler for lmbench, and not much else.
Linus
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