Messages in this thread | | | Date | Mon, 13 Aug 2007 14:30:31 +0200 | From | Jens Axboe <> | Subject | Re: lmbench ctxsw regression with CFS |
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On Mon, Aug 06 2007, Nick Piggin wrote: > > > What CPU did you get these numbers on? Do the indirect calls hurt much > > > on those without an indirect predictor? (I'll try running some tests). > > > > it was on an older Athlon64 X2. I never saw indirect calls really > > hurting on modern x86 CPUs - dont both CPU makers optimize them pretty > > efficiently? (as long as the target function is always the same - which > > it is here.) > > I think a lot of CPUs do. I think ia64 does not. It predicts > based on the contents of a branch target register which has to > be loaded I presume before instructoin fetch reaches the branch. > I don't know if this would hurt or not.
Testing on ia64 showed that the indirect calls in the io scheduler hurt quite a bit, so I'd be surprised if the impact here wasn't an issue there.
-- Jens Axboe
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