lkml.org 
[lkml]   [2010]   [Jan]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC][PATCH 6/8] mm: handle_speculative_fault()


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


\
 
 \ /
  Last update: 2010-01-06 04:31    [W:0.277 / U:0.196 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site