On Sat, Dec 24, 2011 at 05:55:14PM +0700, Nguyen Thai Ngoc Duy wrote:
> On Sat, Dec 24, 2011 at 2:07 PM, Jeff King <peff@xxxxxxxx> wrote:
> > The case where we would most expect the setup cost to be drowned out is
> > using a more complex regex, grepping tree objects. There we have a
> > baseline of:
> >
> > $ time git grep 'a.*c' HEAD >/dev/null
> > real 0m5.684s
> > user 0m5.472s
> > sys 0m0.196s
> >
> > $ time git ls-tree --name-only -r HEAD |
> > xargs git grep 'a.*c' HEAD -- >/dev/null
> > real 0m10.906s
> > user 0m10.725s
> > sys 0m0.240s
> >
> > Here, we still almost double our time. It looks like we don't use the
> > same pathspec matching code in this case. But we do waste a lot of extra
> > time zlib-inflating the trees in "ls-tree", only to do it separately in
> > "grep".
>
> I assume this is gree_tree(), we have another form of pathspec
> matching here: tree_entry_interesting() and it's still a bunch of
> strcmp inside. Does strcmp show up in perf report?
Yes, but not nearly as high. The top of the report is:
+ 32.16% git libc-2.13.so [.] re_search_internal
+ 17.82% git libz.so.1.2.3.4 [.] 0xe986
+ 7.81% git git [.] look_ahead
+ 6.24% git libc-2.13.so [.] __strncmp_sse42
+ 4.08% git git [.] tree_entry_interesting
+ 3.27% git git [.] end_of_line
+ 2.63% git libz.so.1.2.3.4 [.] adler32
+ 1.93% git libz.so.1.2.3.4 [.] inflate
where the strncmps are from[1]:
- 6.24% git libc-2.13.so [.] __strncmp_sse42
- __strncmp_sse42
+ 80.92% grep_tree
+ 19.08% tree_entry_interesting
So we're spending maybe 10% of our time on pathspecs, but most of it is
going to zlib and the actual regex search.
-Peff
[1] Note that this is with -O2, so some of that is from inlined calls.
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