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| author | Nick Piggin <npiggin@kernel.dk> | 2011-01-07 17:50:09 +1100 |
|---|---|---|
| committer | Nick Piggin <npiggin@kernel.dk> | 2011-01-07 17:50:32 +1100 |
| commit | 9d55c369bb5e695e629bc35cba2ef607755b3bee (patch) | |
| tree | d97cd498a67f1f7987d4403ef90e399516a3b8c9 /fs | |
| parent | e1bb57826381199cc79fbf44e9dfeee58fc7b339 (diff) | |
| download | linux-9d55c369bb5e695e629bc35cba2ef607755b3bee.tar.gz linux-9d55c369bb5e695e629bc35cba2ef607755b3bee.tar.bz2 linux-9d55c369bb5e695e629bc35cba2ef607755b3bee.zip | |
fs: implement faster dentry memcmp
The standard memcmp function on a Westmere system shows up hot in
profiles in the `git diff` workload (both parallel and single threaded),
and it is likely due to the costs associated with trapping into
microcode, and little opportunity to improve memory access (dentry
name is not likely to take up more than a cacheline).
So replace it with an open-coded byte comparison. This increases code
size by 8 bytes in the critical __d_lookup_rcu function, but the
speedup is huge, averaging 10 runs of each:
git diff st user sys elapsed CPU
before 1.15 2.57 3.82 97.1
after 1.14 2.35 3.61 96.8
git diff mt user sys elapsed CPU
before 1.27 3.85 1.46 349
after 1.26 3.54 1.43 333
Elapsed time for single threaded git diff at 95.0% confidence:
-0.21 +/- 0.01
-5.45% +/- 0.24%
It's -0.66% +/- 0.06% elapsed time on my Opteron, so rep cmp costs on the
fam10h seem to be relatively smaller, but there is still a win.
Signed-off-by: Nick Piggin <npiggin@kernel.dk>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/dcache.c | 12 |
1 files changed, 3 insertions, 9 deletions
diff --git a/fs/dcache.c b/fs/dcache.c index 2a4ce7dc2306..5699d4c027cb 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1454,9 +1454,7 @@ static struct dentry *__d_instantiate_unique(struct dentry *entry, continue; if (alias->d_parent != entry->d_parent) continue; - if (qstr->len != len) - continue; - if (memcmp(qstr->name, name, len)) + if (dentry_cmp(qstr->name, qstr->len, name, len)) continue; __dget(alias); return alias; @@ -1810,9 +1808,7 @@ seqretry: tlen, tname, name)) continue; } else { - if (tlen != len) - continue; - if (memcmp(tname, str, tlen)) + if (dentry_cmp(tname, tlen, str, len)) continue; } /* @@ -1925,9 +1921,7 @@ struct dentry *__d_lookup(struct dentry *parent, struct qstr *name) tlen, tname, name)) goto next; } else { - if (tlen != len) - goto next; - if (memcmp(tname, str, tlen)) + if (dentry_cmp(tname, tlen, str, len)) goto next; } |