Messages in this thread | | | Date | Wed, 21 Nov 2007 21:09:58 +0100 | From | Ingo Molnar <> | Subject | Re: some thoughts about TSC based delay_tsc() |
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* Marin Mitov <mitov@issp.bas.bg> wrote:
> On Wednesday 21 November 2007 09:27:54 pm you wrote: > > * Marin Mitov <mitov@issp.bas.bg> wrote: > > > Hi Ingo, > > > > > > The patch is quite good ;-) but we forget when it is needed :-( In > > > fact we need it only for PREEMPT SMP kernels - it could hurt > > > PREEMPT UP kernels (no migration possible), so no need for > > > preempt_disable()/preempt_enable(). > > > > > > In short the old version of delay_tsc() is good for UP kernels and > > > NON PREEMPT SMP kernels too. > > > > please reply to the public list, so that discussions do not get lost. > > > > i dont think there's any problem: udelay() is about _wasting_ cycles - > > it's what drivers use for short delays. > > Sure for the thread executing udelay(), but not for the other ready > threads which should also wait till preempt_enable() to grab the same > cpu even for PREEMPT (UP or SMP) kernels (or I misunderstand > something?).
on non-PREEMPT kernels there's no real difference between old and and new code because the kernel is not preemptible. So we can use the new code unconditionally.
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