From: Dave Hansen <dave@sr71.net>
To: Mel Gorman <mgorman@suse.de>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org,
akpm@linux-foundation.org, kirill.shutemov@linux.intel.com,
ak@linux.intel.com, riel@redhat.com, alex.shi@linaro.org,
dave.hansen@linux.intel.com
Subject: Re: [PATCH 2/6] x86: mm: rip out complicated, out-of-date, buggy TLB flushing
Date: Fri, 25 Apr 2014 14:39:57 -0700 [thread overview]
Message-ID: <535AD62D.20509@sr71.net> (raw)
In-Reply-To: <20140424084552.GQ23991@suse.de>
On 04/24/2014 01:45 AM, Mel Gorman wrote:
>> > +/*
>> > + * See Documentation/x86/tlb.txt for details. We choose 33
>> > + * because it is large enough to cover the vast majority (at
>> > + * least 95%) of allocations, and is small enough that we are
>> > + * confident it will not cause too much overhead. Each single
>> > + * flush is about 100 cycles, so this caps the maximum overhead
>> > + * at _about_ 3,000 cycles.
>> > + */
>> > +/* in units of pages */
>> > +unsigned long tlb_single_page_flush_ceiling = 1;
>> > +
> This comment is premature. The documentation file does not exist yet and
> 33 means nothing yet. Out of curiousity though, how confident are you
> that a TLB flush is generally 100 cycles across different generations
> and manufacturers of CPUs? I'm not suggesting you change it or auto-tune
> it, am just curious.
First of all, I changed the units here at some point, and I screwed up
the comments. I meant 100 nanoseconds, *not* cycles.
For the sake of completeness, here are the data on a Westmere CPU. I'm
not _quite_ sure why the <=5 pages cases are so slow per-page compared
to when we're flushing larger numbers of pages. (I also only printed
out the flush sizes with >100 samples):
The overall average was 151ns, and for 6 pages and up it was 107ns.
1 1560658 279861777 avg/page: 179
2 179981 85329139 avg/page: 237
3 99797 146972011 avg/page: 490
4 161470 133072233 avg/page: 206
5 44150 42142670 avg/page: 190
6 17364 12063833 avg/page: 115
7 12325 9899412 avg/page: 114
8 4202 3838077 avg/page: 114
9 811 990320 avg/page: 135
10 4448 4955283 avg/page: 111
11 69051 86723229 avg/page: 114
12 465 642204 avg/page: 115
13 157 226814 avg/page: 111
16 781 1741461 avg/page: 139
17 1506 2778201 avg/page: 108
18 110 211216 avg/page: 106
19 13322 27941893 avg/page: 110
21 1828 4092988 avg/page: 106
24 1566 4057605 avg/page: 107
25 246 646463 avg/page: 105
29 411 1275101 avg/page: 106
33 3191 11775818 avg/page: 111
52 3096 17297873 avg/page: 107
65 2244 15349445 avg/page: 105
129 2278 33246120 avg/page: 113
240 12181 305529055 avg/page: 104
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next prev parent reply other threads:[~2014-04-25 21:40 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-21 18:24 [PATCH 0/6] x86: rework tlb range flushing code Dave Hansen
2014-04-21 18:24 ` [PATCH 1/6] x86: mm: clean up tlb " Dave Hansen
2014-04-22 16:53 ` Rik van Riel
2014-04-24 8:33 ` Mel Gorman
2014-04-21 18:24 ` [PATCH 2/6] x86: mm: rip out complicated, out-of-date, buggy TLB flushing Dave Hansen
2014-04-22 16:54 ` Rik van Riel
2014-04-24 8:45 ` Mel Gorman
2014-04-24 16:58 ` Dave Hansen
2014-04-24 18:00 ` Mel Gorman
2014-04-25 21:39 ` Dave Hansen [this message]
2014-04-21 18:24 ` [PATCH 3/6] x86: mm: fix missed global TLB flush stat Dave Hansen
2014-04-22 17:15 ` Rik van Riel
2014-04-24 8:49 ` Mel Gorman
2014-04-21 18:24 ` [PATCH 4/6] x86: mm: trace tlb flushes Dave Hansen
2014-04-22 21:19 ` Rik van Riel
2014-04-24 10:14 ` Mel Gorman
2014-04-24 20:42 ` Dave Hansen
2014-04-21 18:24 ` [PATCH 5/6] x86: mm: new tunable for single vs full TLB flush Dave Hansen
2014-04-22 21:31 ` Rik van Riel
2014-04-24 10:37 ` Mel Gorman
2014-04-24 17:25 ` Dave Hansen
2014-04-24 17:53 ` Rik van Riel
2014-04-24 22:03 ` Dave Hansen
2014-07-07 17:43 ` Dave Hansen
2014-07-08 0:43 ` Alex Shi
2014-04-21 18:24 ` [PATCH 6/6] x86: mm: set TLB flush tunable to sane value (33) Dave Hansen
2014-04-22 21:33 ` Rik van Riel
2014-04-24 10:46 ` Mel Gorman
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