Re: [PATCH] mm, vmstat: Use cond_resched only when !CONFIG_PREEMPT

[Minchan Kim]

On Mon, May 30, 2011 at 10:59:04PM +0600, Rakib Mullick 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@xxxxxxxxx>

Let me ask questions.

1. What's bad if we call cond_resched on CONFIG_PREEMPT?
   Is refresh_cpu_vm_stats a hot path?
2. There is no help to call explicit scheduling point on CONFIG_PREEMPTION?
 
We used cond_resched without any ifdef/endif of CONFIG_PREEMPT.
In addtion, cond_resched includes __might_sleep which is debugging help for lock.
So I hope let it be if you have a big concern.

-- 
Kind regards
Meinchan Kim
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