Doing an oprofile run on the result of my git rev-list memory leak fixes
and tree parsing cleanups, I was surprised by the third-highest entry
being
samples % image name app name symbol name
179751 2.7163 libc-2.4.so libc-2.4.so _IO_vfscanf@@GLIBC_2.4
where that 2.7% is actually more than 5% of one CPU, because this was run
on a dual CPU setup with the other CPU just being idle.
That seems to all be from the use of 'sscanf(tree, "%o", &mode)' for the
tree buffer parsing.
So do the trivial octal parsing by hand, which also gives us where the
first space in the string is (and thus where the pathname starts) so we
can get rid of the "strchr(tree, ' ')" call too.
This brings the "git rev-list --all --objects" time down from 63 seconds
to 55 seconds on the historical kernel archive for me, so it's quite
noticeable - tree parsing is a lot of what we end up doing when following
all the objects.
[ I also see a 5% speedup on a full "git fsck-objects" on the current
kernel archive, so that sscanf() really does seem to have hurt our
performance by a surprising amount ]
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxx>
---
tree-walk.c | 21 ++++++++++++++++++---
1 files changed, 18 insertions(+), 3 deletions(-)
diff --git a/tree-walk.c b/tree-walk.c
index 9f7abb7..3922058 100644
--- a/tree-walk.c
+++ b/tree-walk.c
@@ -47,18 +47,33 @@ void update_tree_entry(struct tree_desc
desc->size = size - len;
}
+static const char *get_mode(const char *str, unsigned int *modep)
+{
+ unsigned char c;
+ unsigned int mode = 0;
+
+ while ((c = *str++) != ' ') {
+ if (c < '0' || c > '7')
+ return NULL;
+ mode = (mode << 3) + (c - '0');
+ }
+ *modep = mode;
+ return str;
+}
+
const unsigned char *tree_entry_extract(struct tree_desc *desc, const char **pathp, unsigned int *modep)
{
void *tree = desc->buf;
unsigned long size = desc->size;
int len = strlen(tree)+1;
const unsigned char *sha1 = tree + len;
- const char *path = strchr(tree, ' ');
+ const char *path;
unsigned int mode;
- if (!path || size < len + 20 || sscanf(tree, "%o", &mode) != 1)
+ path = get_mode(tree, &mode);
+ if (!path || size < len + 20)
die("corrupt tree file");
- *pathp = path+1;
+ *pathp = path;
*modep = canon_mode(mode);
return sha1;
}
-
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