On 11/15/2013 10:47 AM, Andrea Arcangeli wrote:
Hi,
1/3 is a bugfix so it should be applied more urgently. 1/3 is not as
fast as the current upstream code in the hugetlbfs + directio extreme
8GB/sec benchmark (but 3/3 should fill the gap later). The code is
identical to the one I posted in v1 just rebased on upstream and was
developed in collaboration with Khalid who already tested it.
2/3 and 3/3 had very little testing yet, and they're incremental
optimization. 2/3 is minor and most certainly worth applying later.
3/3 instead complicates things a bit and adds more branches to the THP
fast paths, so it should only be applied if the benchmarks of
hugetlbfs + directio show that it is very worthwhile (that has not
been verified yet). If it's not worthwhile 3/3 should be dropped (and
the gap should be filled in some other way if the gap is not caused by
the _mapcount mangling as I guessed). Ideally this should bring even
more performance than current upstream code, as current upstream code
still increased the _mapcount in gup_fast by mistake, while this
eliminates the locked op on the tail page cacheline in gup_fast too
(which is required for correctness too).
Hi Andrea,
I ran directio benchmark and here are the performance numbers (MBytes/sec):
Block size 3.12 3.12+patch 1 3.12+patch 1,2,3
---------- ---- ------------ ----------------
1M 8467 8114 7648
64K 4049 4043 4175
Performance numbers with 64K reads look good but there is further
deterioration with 1M reads.
--
Khalid
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