Messages in this thread | | | Date | Tue, 5 Jan 2010 19:27:07 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: [RFC][PATCH 6/8] mm: handle_speculative_fault() |
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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
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