1) consistently use "unsigned int" for dentry name length,
2) reuse subtraction result for return value, exact value doesn't matter
because function is only used in boolean context,
3) use *p++ idiom for even better code.
All of this results in performance speedup of "git diff"
which is way out of statistical error (0.4% vs 0.15% of 3 sigma):
$ PAGER= perf stat -r 256 git-diff
Performance counter stats for 'git-diff' (256 runs):
115.033582 task-clock # 0.993 CPUs utilized ( +- 0.06% )
0 context-switches # 0.000 M/sec ( +- 17.95% )
0 CPU-migrations # 0.000 M/sec ( +- 19.47% )
2,321 page-faults # 0.020 M/sec ( +- 0.00% )
384,540,991 cycles # 3.343 GHz ( +- 0.05% )
121,833,562 stalled-cycles-frontend # 31.68% frontend cycles idle ( +- 0.16% )
51,731,784 stalled-cycles-backend # 13.45% backend cycles idle ( +- 0.37% )
586,327,441 instructions # 1.52 insns per cycle
# 0.21 stalled cycles per insn ( +- 0.00% )
155,449,246 branches # 1351.338 M/sec ( +- 0.00% )
542,511 branch-misses # 0.35% of all branches ( +- 0.07% )
0.115856505 seconds time elapsed ( +- 0.06% )
----------------------------------
after
Performance counter stats for 'git-diff' (256 runs):
114.486145 task-clock # 0.993 CPUs utilized ( +- 0.05% )
0 context-switches # 0.000 M/sec ( +- 15.46% )
0 CPU-migrations # 0.000 M/sec ( +- 20.06% )
2,282 page-faults # 0.020 M/sec ( +- 0.00% )
382,725,382 cycles # 3.343 GHz ( +- 0.05% )
119,808,563 stalled-cycles-frontend # 31.30% frontend cycles idle ( +- 0.15% )
51,780,030 stalled-cycles-backend # 13.53% backend cycles idle ( +- 0.33% )
585,114,727 instructions # 1.53 insns per cycle
# 0.20 stalled cycles per insn ( +- 0.00% )
155,146,262 branches # 1355.153 M/sec ( +- 0.00% )
526,739 branch-misses # 0.34% of all branches ( +- 0.12% )
0.115315823 seconds time elapsed ( +- 0.05% )
Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
---
fs/dcache.c | 6 +++---
include/linux/dcache.h | 14 +++++++-------
2 files changed, 10 insertions(+), 10 deletions(-)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1368,7 +1368,7 @@ static struct dentry *__d_instantiate_unique(struct dentry *entry,
struct inode *inode)
{
struct dentry *alias;
- int len = entry->d_name.len;
+ unsigned int len = entry->d_name.len;
const char *name = entry->d_name.name;
unsigned int hash = entry->d_name.hash;
@@ -1750,7 +1750,7 @@ struct dentry *__d_lookup_rcu(struct dentry *parent, struct qstr *name,
hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
struct inode *i;
const char *tname;
- int tlen;
+ unsigned int tlen;
if (dentry->d_name.hash != hash)
continue;
@@ -1869,7 +1869,7 @@ struct dentry *__d_lookup(struct dentry *parent, struct qstr *name)
hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
const char *tname;
- int tlen;
+ unsigned int tlen;
if (dentry->d_name.hash != hash)
continue;
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -51,18 +51,18 @@ extern struct dentry_stat_t dentry_stat;
* Compare 2 name strings, return 0 if they match, otherwise non-zero.
* The strings are both count bytes long, and count is non-zero.
*/
-static inline int dentry_cmp(const unsigned char *cs, size_t scount,
- const unsigned char *ct, size_t tcount)
+static inline int dentry_cmp(const unsigned char *cs, unsigned int scount,
+ const unsigned char *ct, unsigned int tcount)
{
int ret;
- if (scount != tcount)
- return 1;
+
+ ret = scount - tcount;
+ if (ret)
+ return ret;
do {
- ret = (*cs != *ct);
+ ret = *cs++ - *ct++;
if (ret)
break;
- cs++;
- ct++;
tcount--;
} while (tcount);
return ret;
--
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