Messages in this thread | | | Date | Mon, 21 Aug 2017 15:07:57 +0100 | From | Juri Lelli <> | Subject | Re: [PATCH v8 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() |
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On 21/08/17 15:56, Peter Zijlstra wrote: > On Mon, Aug 21, 2017 at 02:44:58PM +0100, Juri Lelli wrote: > > > Also, I'm not sure what Peter meant with > > > > "But still this isn't quite right, because when we consider this for SMT > > (as was the intent here) we'll happily occupy a full sibling core over > > finding an empty one." > > Consider a 4 core, SMT2 system: > > LLC [0 - 7] > > SMT [0,1] [2,3] [4,5] [6,7] > > If we do a wake-up on CPU0, we'll find CPU1, mark that as fallback, > continue up the domain tree, exclude 0,1 from 0-7 and find CPU2. > > A next wakeup on CPU0 does the same and will find CPU3, fully loading > that core, instead of considering CPU4 first. >
Ah, right, I see. Thanks for explaining.
Byungchul, maybe you could add this explanation as a comment?
> Doing this 'right' is difficult and expensive :-/ >
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