Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock

[Peter Zijlstra]

On Wed, Aug 21, 2013 at 01:35:51PM +0200, Oleg Nesterov wrote:
> On 08/21, Peter Zijlstra wrote:

> > Yes its the right rq, but the wrong time.
> 
> Hmm. Just in case, it is not that I think this patch really makes sense,
> but I'd like to understand why do you think it is wrong.
 
> But it is not "after it switches out", it is after it switched back.

D'uh I was being particularly dense it seems :/

Yes I think it is correct. You're now trading two atomic ops on a
different cacheline than rq->lock for one atomic op on the rq->lock.

Might be a win, esp. since hopefully there's a fair chance its the same
runqueue.


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