Messages in this thread | | | Date | Tue, 20 Aug 2013 08:31:53 -0700 | From | Arjan van de Ven <> | Subject | Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock |
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On 8/20/2013 1:44 AM, Peter Zijlstra wrote: > On Tue, Aug 20, 2013 at 03:59:36PM +0900, Fernando Luis Vázquez Cao wrote: >> That said, if deemed acceptable, option A is the one I would >> choose. > > Right, so I think we can do A without much extra cost mostly because we > already have 2 atomics in the io_schedule() path. If we replace those > two atomic operations with locks and modify nr_iowait and the other > stats under the same lock, and ensure all those variables (including the > lock) live in the same cacheline we should have the same cost we have > now. > > Of course, if we can get away with completely removing all of that > (which I think Arjan suggested was a real possibility) then that would > be ever so much better still :-)
I'm quite ok with removing that.
however note that "top" also reports per cpu iowait... and that's a userspace expectation
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