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Date: Wed, 8 Sep 2010 16:48:18 +0100 From: Will Newton <will.newton@...il.com> To: fabio de francesco <fabio@...anix.org> Cc: LKML <linux-kernel@...r.kernel.org> Subject: Re: [process scheduler] Possible bug in context_swich()? On Wed, Sep 8, 2010 at 4:28 PM, fabio de francesco <fabio@...anix.org> wrote: > Dear List, > > My previous mails to you have gone unheard... my last chance... > > 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. Hi fabio, The logic was changed in commit 710390d90f143a9ebb87a475215140f426792efd on the basis of a branch hint profiling run. It would guess previous logic was more likely to be correct, unless one is often scheduling between kernel threads, but maybe that happens more often than I expect. I would suggest trying the branch tracer yourself if you think the current code is wrong for your workload, the config option is PROFILE_ANNOTATED_BRANCHES. I would suggest not profiling the boot process (which will have predominantly kernel threads) and not profiling on an idle system (which may also be relatively heavy on kernel threads). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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