Messages in this thread | | | Date | Tue, 31 May 2011 09:58:40 +0600 | Subject | Re: [PATCH] mm, vmstat: Use cond_resched only when !CONFIG_PREEMPT | From | Rakib Mullick <> |
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On Tue, May 31, 2011 at 9:18 AM, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote: > On Tue, 31 May 2011 09:13:47 +0600 > Rakib Mullick <rakib.mullick@gmail.com> wrote: > >> On Tue, May 31, 2011 at 5:38 AM, KAMEZAWA Hiroyuki >> <kamezawa.hiroyu@jp.fujitsu.com> wrote: >> > On Mon, 30 May 2011 22:59:04 +0600 >> > Rakib Mullick <rakib.mullick@gmail.com> wrote: >> > >> >> commit 468fd62ed9 (vmstats: add cond_resched() to refresh_cpu_vm_stats()) added cond_resched() in refresh_cpu_vm_stats. Purpose of that patch was to allow other threads to run in non-preemptive case. This patch, makes sure that cond_resched() gets called when !CONFIG_PREEMPT is set. In a preemptiable kernel we don't need to call cond_resched(). >> >> >> >> Signed-off-by: Rakib Mullick <rakib.mullick@gmail.com> >> > >> > Hmm, what benefit do we get by adding this extra #ifdef in the code directly ? >> > Other cond_resched() callers are not guilty in !CONFIG_PREEMPT ? >> > >> Well, in preemptible kernel this context will get preempted if >> requires, so we don't need cond_resched(). If you checkout the git log >> of the mentioned commit, you'll find the explanation. It says: >> "Adding a cond_resched() to allow other threads to run in the >> non-preemptive >> case." >> > > IOW, my question is "why only this cond_resched() should be fixed ?"
cond_resched() forces this thread to be scheduled. I'm just trying pointing out the use of cond_resched(), until unless I'm not missing anything.
> What's bad with all cond_resched() in the kernel as no-op in CONFIG_PREEMPT ? > cond_resched() basically checks whether it needs to be scheduled or not. But, we know in advance that we don't need cond_resched in CONFIG_PREEMPT.
Thanks, Rakib
> Thanks, > -Kame > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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