From mboxrd@z Thu Jan 1 00:00:00 1970 Received: by ug-out-1314.google.com with SMTP id 34so1609548ugf.19 for ; Thu, 27 Nov 2008 05:10:24 -0800 (PST) Message-ID: <492E9C3C.9050507@gmail.com> Date: Thu, 27 Nov 2008 15:10:20 +0200 From: =?ISO-8859-1?Q?T=F6r=F6k_Edwin?= MIME-Version: 1.0 Subject: Re: [RFC v1][PATCH]page_fault retry with NOPAGE_RETRY References: <604427e00811251042t1eebded6k9916212b7c0c2ea0@mail.gmail.com> <20081126123246.GB23649@wotan.suse.de> <492DAA24.8040100@google.com> <20081127085554.GD28285@wotan.suse.de> <492E6849.6090205@google.com> <492E8708.4060601@gmail.com> <20081127120330.GM28285@wotan.suse.de> <492E90BC.1090208@gmail.com> <20081127123926.GN28285@wotan.suse.de> <492E97FA.5000804@gmail.com> <20081127130525.GO28285@wotan.suse.de> In-Reply-To: <20081127130525.GO28285@wotan.suse.de> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: Mike Waychison , Ying Han , Ingo Molnar , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm , David Rientjes , Rohit Seth , Hugh Dickins , Peter Zijlstra , "H. Peter Anvin" List-ID: On 2008-11-27 15:05, Nick Piggin wrote: > On Thu, Nov 27, 2008 at 02:52:10PM +0200, Torok Edwin wrote: > >> On 2008-11-27 14:39, Nick Piggin wrote: >> >>> And then you also get the advantages of reduced contention on other >>> shared locks and resources. >>> >>> >> Thanks for the tips, but lets get back to the original question: >> why don't I see any performance improvement with the fault-retry patches? >> > > Because as you said, your app is CPU bound and page faults aren't needing > to sleep very much. There is too much contention on the write side, rather > than too much contention/hold time on the read side. > > > >> My testcase only compares reads file with mmap, vs. reading files with >> read, with different number of threads. >> Leaving aside other reasons why mmap is slower, there should be some >> speedup by running 4 threads vs 1 thread, but: >> >> 1 thread: read:27,18 28.76 >> 1 thread: mmap: 25.45, 25.24 >> 2 thread: read: 16.03, 15.66 >> 2 thread: mmap: 22.20, 20.99 >> 4 thread: read: 9.15, 9.12 >> 4 thread: mmap: 20.38, 20.47 >> >> The speed of 4 threads is about the same as for 2 threads with mmap, yet >> with read it scales nicely. >> And the patch doesn't seem to improve scalability. >> How can I find out if the patch works as expected? [i.e. verify that >> faults are actually retried, and that they don't keep the semaphore locked] >> > > Yeah, that workload will be completely contended on the mmap_sem write-side > if the files are in cache. The google patch won't help at all in that > case. > Ok. Sorry for hijacking the thread, my testcase is not a good testcase for what this patch tries to solve. Best regards, --Edwin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org