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Date: Wed, 6 Jan 2010 12:56:25 +0900 From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Minchan Kim <minchan.kim@...il.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Peter Zijlstra <peterz@...radead.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, cl@...ux-foundation.org, "hugh.dickins" <hugh.dickins@...cali.co.uk>, Nick Piggin <nickpiggin@...oo.com.au>, Ingo Molnar <mingo@...e.hu> Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault() On Tue, 5 Jan 2010 19:27:07 -0800 (PST) Linus Torvalds <torvalds@...ux-foundation.org> wrote: > > > 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). > It's zone->lock, I guess. My test program avoids pgtable lock problem. > 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. > yes. > > 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@...extal 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@...extal 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. > I'd like to stop updating my patch and wait and see how this issue goes. Anyway, test on a big machine is appreciated because I cat test only on 2 sockets host. Thanks, -Kame -- 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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