perf reports memcpy at the the 6th position [1] in "git status -uno"
using index v4, and strbuf_remove() in expand_name_field() accounts
for 25% of that. What we need here is a simple string cut and a
cheaper strbuf_setlen() should be enough. After this change, memcpy
drops down to the 13th position [2] and is dominated by
read_index_from.
[1] before
+ 15.74% git git [.] blk_SHA1_Block
+ 13.22% git [kernel.kallsyms] [k] link_path_walk
+ 10.91% git [kernel.kallsyms] [k] __d_lookup
+ 8.17% git [kernel.kallsyms] [k] strncpy_from_user
+ 4.75% git [kernel.kallsyms] [k] memcmp
+ 2.42% git libc-2.11.2.so [.] memcpy
[2] after
+ 16.30% git git [.] blk_SHA1_Block
+ 13.43% git [kernel.kallsyms] [k] link_path_walk
+ 11.45% git [kernel.kallsyms] [k] __d_lookup
+ 8.73% git [kernel.kallsyms] [k] strncpy_from_user
+ 5.14% git [kernel.kallsyms] [k] memcmp
+ 2.29% git [kernel.kallsyms] [k] do_lookup
+ 2.21% git libc-2.11.2.so [.] 0x6daf6
+ 1.98% git [kernel.kallsyms] [k] _atomic_dec_and_lock
+ 1.98% git [kernel.kallsyms] [k] _raw_spin_lock
+ 1.86% git [kernel.kallsyms] [k] acl_permission_check
+ 1.61% git [kernel.kallsyms] [k] kmem_cache_free
+ 1.59% git git [.] unpack_trees
+ 1.47% git libc-2.11.2.so [.] memcpy
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx>
---
I was after something else when I noticed this. Seems like a simple
and safe change.
read-cache.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/read-cache.c b/read-cache.c
index 827ae55..8c443aa 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1354,7 +1354,7 @@ static unsigned long expand_name_field(struct strbuf *name, const char *cp_)
if (name->len < len)
die("malformed name field in the index");
- strbuf_remove(name, name->len - len, len);
+ strbuf_setlen(name, name->len - len);
for (ep = cp; *ep; ep++)
; /* find the end */
strbuf_add(name, cp, ep - cp);
--
1.8.2.83.gc99314b
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