On Fri, Aug 24, 2018 at 05:37:20PM +0200, Duy Nguyen wrote:
> Since we're cutting corners to speed things up, could you try
> something like this?
>
> I notice that reading v4 is significantly slower than v2 and
> apparently strlen() (at least from glibc) is much cleverer and at
> least gives me a few percentage time saving.
>
> diff --git a/read-cache.c b/read-cache.c
> index 7b1354d759..d10cccaed0 100644
> --- a/read-cache.c
> +++ b/read-cache.c
> @@ -1755,8 +1755,7 @@ 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);
> - for (ep = cp; *ep; ep++)
> - ; /* find the end */
> + ep = cp + strlen(cp);
> strbuf_add(name, cp, ep - cp);
> return (const char *)ep + 1 - cp_;
> }
No try this instead. It's half way back to v2 numbers for me (tested
with "test-tool read-cache 100" on webkit.git). For the record, v4 is
about 30% slower than v2 in my tests.
We could probably do better too. Instead of preparing the string in a
separate buffer (previous_name_buf), we could just assemble it directly
to the newly allocated "ce".
-- 8< --
diff --git a/read-cache.c b/read-cache.c
index 7b1354d759..237f60a76c 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1754,9 +1754,8 @@ 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);
- for (ep = cp; *ep; ep++)
- ; /* find the end */
+ strbuf_setlen(name, name->len - len);
+ ep = cp + strlen(cp);
strbuf_add(name, cp, ep - cp);
return (const char *)ep + 1 - cp_;
}
-- 8< --
