Hi,
On Sun, 18 Mar 2007, Linus Torvalds wrote:
> All the top profiling hits are about generating the patches and
> assigning blame:
>
> samples % image name app name symbol name
> 470352 15.5813 git git xdl_hash_record
I felt a little left out in all that performance slashing, and so I
thought maybe, just maybe, a small change in xdl_hash_record() can do
wonders (since it _is_ really simple, but still takes almost a 6th of the
CPU time). I don't have a proper test case setup, so maybe you want to try
this:
-- snipsnap --
[PATCH] xdiff/xutils.c(xdl_hash_record): factor out whitespace handling
Since in at least one use case, xdl_hash_record() takes over 15% of the
CPU time, it makes sense to even micro-optimize it. For many cases, no
whitespace special handling is needed, and in these cases we should not
even bother to check for whitespace in _every_ iteration of the loop.
Signed-off-by: Johannes Schindelin <Johannes.Schindelin@xxxxxx>
---
Please do not consider this patch _unless_ it is proven to enhance
the profile statistics substantially.
xdiff/xutils.c | 22 ++++++++++++++++++++--
1 files changed, 20 insertions(+), 2 deletions(-)
diff --git a/xdiff/xutils.c b/xdiff/xutils.c
index 3653864..bf91c0f 100644
--- a/xdiff/xutils.c
+++ b/xdiff/xutils.c
@@ -236,12 +236,13 @@ int xdl_recmatch(const char *l1, long s1, const char *l2, long s2, long flags)
return 0;
}
-unsigned long xdl_hash_record(char const **data, char const *top, long flags) {
+static unsigned long xdl_hash_record_with_whitespace(char const **data,
+ char const *top, long flags) {
unsigned long ha = 5381;
char const *ptr = *data;
for (; ptr < top && *ptr != '\n'; ptr++) {
- if (isspace(*ptr) && (flags & XDF_WHITESPACE_FLAGS)) {
+ if (isspace(*ptr)) {
const char *ptr2 = ptr;
while (ptr + 1 < top && isspace(ptr[1])
&& ptr[1] != '\n')
@@ -270,6 +271,23 @@ unsigned long xdl_hash_record(char const **data, char const *top, long flags) {
}
+unsigned long xdl_hash_record(char const **data, char const *top, long flags) {
+ unsigned long ha = 5381;
+ char const *ptr = *data;
+
+ if (flags & XDF_WHITESPACE_FLAGS)
+ return xdl_hash_record_with_whitespace(data, top, flags);
+
+ for (; ptr < top && *ptr != '\n'; ptr++) {
+ ha += (ha << 5);
+ ha ^= (unsigned long) *ptr;
+ }
+ *data = ptr < top ? ptr + 1: ptr;
+
+ return ha;
+}
+
+
unsigned int xdl_hashbits(unsigned int size) {
unsigned int val = 1, bits = 0;
-
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