From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with ESMTP id 69C2D6B006A for ; Tue, 5 Jan 2010 22:27:46 -0500 (EST) Date: Tue, 5 Jan 2010 19:27:07 -0800 (PST) From: Linus Torvalds Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault() In-Reply-To: <20100106115233.5621bd5e.kamezawa.hiroyu@jp.fujitsu.com> Message-ID: References: <20100104182429.833180340@chello.nl> <20100104182813.753545361@chello.nl> <20100105092559.1de8b613.kamezawa.hiroyu@jp.fujitsu.com> <28c262361001042029w4b95f226lf54a3ed6a4291a3b@mail.gmail.com> <20100105134357.4bfb4951.kamezawa.hiroyu@jp.fujitsu.com> <20100105143046.73938ea2.kamezawa.hiroyu@jp.fujitsu.com> <20100105163939.a3f146fb.kamezawa.hiroyu@jp.fujitsu.com> <20100106092212.c8766aa8.kamezawa.hiroyu@jp.fujitsu.com> <20100106115233.5621bd5e.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: Minchan Kim , Peter Zijlstra , "Paul E. McKenney" , Peter Zijlstra , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , cl@linux-foundation.org, "hugh.dickins" , Nick Piggin , Ingo Molnar List-ID: On Wed, 6 Jan 2010, KAMEZAWA Hiroyuki wrote: > > My host boots successfully. Here is the result. Hey, looks good. It does have that 3% trylock overhead: 3.17% multi-fault-all [kernel] [k] down_read_trylock but that doesn't seem excessive. Of course, your other load with MADV_DONTNEED seems to be horrible, and has some nasty spinlock issues, but that looks like a separate deal (I assume that load is just very hard on the pgtable lock). That said, profiles are hard to compare performance with - the main thing that matters for performance is not how the profile looks, but how it actually performs. So: > Then, the result is much improved by XADD rwsem. > > In above profile, rwsem is still there. > But page-fault/sec is good. I hope some "big" machine users join to the test. That "page-fault/sec" number is ultimately the only thing that matters. > Here is peformance counter result of DONTNEED test. Counting the number of page > faults in 60 sec. So, bigger number of page fault is better. > > [XADD rwsem] > [root@bluextal memory]# /root/bin/perf stat -e page-faults,cache-misses --repeat 5 ./multi-fault-all 8 > > Performance counter stats for './multi-fault-all 8' (5 runs): > > 41950863 page-faults ( +- 1.355% ) > 502983592 cache-misses ( +- 0.628% ) > > 60.002682206 seconds time elapsed ( +- 0.000% ) > > [my patch] > [root@bluextal memory]# /root/bin/perf stat -e page-faults,cache-misses --repeat 5 ./multi-fault-all 8 > > Performance counter stats for './multi-fault-all 8' (5 runs): > > 35835485 page-faults ( +- 0.257% ) > 511445661 cache-misses ( +- 0.770% ) > > 60.004243198 seconds time elapsed ( +- 0.002% ) > > Ah....xadd-rwsem seems to be faster than my patch ;) Hey, that sounds great. NOTE! My patch really could be improved. In particular, I suspect that on x86-64, we should take advantage of the 64-bit counter, and use a different RW_BIAS. That way we're not limited to 32k readers, which _could_ otherwise be a problem. So consider my rwsem patch to be purely preliminary. Now that you've tested it, I feel a lot better about it being basically correct, but it has room for improvement. Linus -- 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