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Date: Wed, 25 Feb 2009 14:49:37 +1100 From: Nick Piggin <nickpiggin@...oo.com.au> To: Dave Hansen <dave@...ux.vnet.ibm.com> Cc: Salman Qazi <sqazi@...gle.com>, linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>, "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>, Dave Hansen <haveblue@...ibm.com>, Linus Torvalds <torvalds@...ux-foundation.org> Subject: Re: Another Performance Regression in write() syscall On Wednesday 25 February 2009 03:58:52 Dave Hansen wrote: > On Tue, 2009-02-24 at 19:47 +1100, Nick Piggin wrote: > > On Tuesday 24 February 2009 17:25:45 Dave Hansen wrote: > > > On Mon, 2009-02-23 at 22:05 -0800, Salman Qazi wrote: > > > > Analysis of profile data has led us to believe that the commit > > > > 3d733633a633065729c9e4e254b2e5442c00ef7e has caused a performance > > > > regression. This commit provides for tracking of writers so that > > > > read only bind mounts function correctly. > > > > > > > > We can verify this regression by applying the following patch to > > > > partially disable the above-mentioned commit and then running the > > > > fstime component of Unixbench. The settings used were 256 byte > > > > writes with MAX_BLOCK of 2000. > > > > > > I'm a bit surprised that write() is what is regressing. Unless I > > > screwed up, we do all the expensive accounting at open()/close() time. > > > Is this a test that gets run in parallel on multiple cpus? > > > > Don't forget touch_atime... > > Yeah, that's a good point. Are we sure that's what is happening here, > though? That's one thing a profile would hopefully help with. > > > Still, open/close isn't unimportant either. > > Yeah, that's true. But, what I noticed was that all of the other > open/close activity masked out any overhead from mnt_want/drop_write() > since a big chunk of the overhead was just going and bringing the > vfsmount pieces into the cache. That's very true. > > > Could you take a look at Nick's patches to speed this stuff up? > > > > > > http://thread.gmane.org/gmane.linux.file-systems/28186 > > > > > > We may need to dust those off, although I'm still a bit worried about > > > the complexities of open-coding all the barriers. > > > > I really need to do something about trying to push them upstream again > > actually because we've got them in SLES11 tree. > > Were the patches that you integrated any different from the ones you > posted a few months ago? Don't think they were significantly changed. I'll take another look and repost them. -- 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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