Messages in this thread Patch in this message | | | Subject | Re: [process scheduler] Possible bug in context_swich()? | From | Peter Zijlstra <> | Date | Wed, 08 Sep 2010 17:54:18 +0200 |
| |
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:
10420275 170645395 94 context_switch sched.c 3043 10408421 171098521 94 context_switch sched.c 3050
Signed-off-by: Tim Blechmann <tim@klingt.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Mike Galbraith <efault@gmx.de> Cc: Paul Mackerras <paulus@samba.org> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> LKML-Reference: <4B0BBB9F.6080304@klingt.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/sched.c b/kernel/sched.c index 93474a7..010d5e1 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2829,14 +2829,14 @@ context_switch(struct rq *rq, struct task_struct *prev, */ arch_start_context_switch(prev); - if (unlikely(!mm)) { + if (likely(!mm)) { next->active_mm = oldmm; atomic_inc(&oldmm->mm_count); enter_lazy_tlb(oldmm, next); } else switch_mm(oldmm, mm, next); - if (unlikely(!prev->mm)) { + if (likely(!prev->mm)) { prev->active_mm = NULL; rq->prev_mm = oldmm; }
| |