Messages in this thread | | | Subject | Re: [process scheduler] Possible bug in context_swich()? | From | Mike Galbraith <> | Date | Thu, 09 Sep 2010 04:32:19 +0200 |
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On Wed, 2010-09-08 at 17:54 +0200, Peter Zijlstra wrote: > On Wed, 2010-09-08 at 17:28 +0200, fabio de francesco wrote: > > > In context_switch() (in linux/kernel/sched.c), starting with release 2.6.33, > > two "unlikely" macro have been changed to "likely". I think the previous > > logic was right while the latter is wrong. > > > > In case I am missing something I, please, ask someone to explain the above > > mentioned inversion of logic through releases. > > It helps if you CC people, LKML alone is a bit of a gamble. > > git blame kernel/sched.c, will tell you that the change you refer to > comes from: > > commit 710390d90f143a9ebb87a475215140f426792efd > Author: Tim Blechmann <tim@klingt.org> > Date: Tue Nov 24 11:55:27 2009 +0100 > > sched: Optimize branch hint in context_switch() > > Branch hint profiling on my nehalem machine showed over 90% > incorrect branch hints:
That change never made any sense to me, seems Tim must have been measuring a kthread load. I benched at the time, and saw absolutely zero difference one way or the other wrt max ctx rate on my Q6600.
-Mike
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