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Date: Thu, 9 Feb 2012 09:59:48 -0800 From: Tejun Heo <tj@...nel.org> To: Shaohua Li <shaohua.li@...el.com> Cc: Linus Torvalds <torvalds@...ux-foundation.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() Hello, On Thu, Feb 09, 2012 at 02:22:32PM +0800, Shaohua Li wrote: > >> Tried all the options, the regression still exists. Any new idea? > >> I'll spend some time on it if I can get anything > > > > Can you please try the following one? Thanks a lot! > doesn't work. > I also double confirmed b2efa05265d62 causes the regression I'll soon send a RCU based version. I'm still having trouble reproducing the regression tho. I've tried a few different things. * Heavy thrashing: Disk IO dominates everything and CPUs aren't too busy. While how swap behaves affects completion time, I don't see how CPU locking issue comes into play at all under this circumstance. * Some swap load: Simulated w/ 1G memory limit and buliding defconfig kernel in tmpfs. Swap grows to a couple hundred megabytes but build time is still dominated by CPU. I didn't see any meanginful difference before and after the commit - both in terms of wallclock and CPU times. Maybe these two were too extreme to show the problem and I need to push memory limit a bit further, but it would be great if you can give me a bit more details about your testing. * How much memory does the machine have? How is the tmpfs setup and filled up? What's the size of the tmpfs and the output of "free -m" right before test starts? While the test is running, how occupied are the CPUs? On test completion, what's the output of "free -m"? * 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? Thanks. -- tejun -- 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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