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Date: Fri, 10 Feb 2012 11:09:44 +0800 From: Shaohua Li <shaohua.li@...el.com> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>, Vivek Goyal <vgoyal@...hat.com>, lkml <linux-kernel@...r.kernel.org>, Knut Petersen <Knut_Petersen@...nline.de>, mroos@...ux.ee Subject: Re: [PATCH] block: strip out locking optimization in put_io_context() 2012/2/10 Linus Torvalds <torvalds@...ux-foundation.org>: > On Thu, Feb 9, 2012 at 9:59 AM, Tejun Heo <tj@...nel.org> wrote: >> >> * What exactly is the test and what do you measure? What does "12% >> regression" mean? Is it wallclock time or CPU time? If it's CPU >> time, does systime increase dominate the regression? > > Shaohua, it might be interesting to see a profile of the bad case. > > Now, quite often these kinds of things don't show anything at all - > it's just due to cache issues and there's no obvious "we hold spinlock > X for 15 seconds total". But if it's actual lock contention rather > than just "more scheduling of worker threads", it should show up in > the profile quite clearly. > > That said, I do think the RCU approach is the right one. The whole > delayed deallocation (and the replacement patch with rwlocks) really > smells like "badly done RCU-like behavior" to me. Appears not a lock contention issue. The system is quite idle, about 20% busy. And top shows no cpu is very busy. Before test runs, the system has about 2G free memory (from vmstat) system and user time isn't changed. only real time becomes longer. This suggests IO is slower or there is more IO. But vmstat and iostat data doesn't show significant difference between the good and bad cases. There might be some access pattern changed which makes swap no efficient or working set is wrongly swaped out. -- 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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