On Tue, Mar 25, 2014 at 01:23:20PM +0400, Kirill Smelkov wrote:
> On Mon, Mar 24, 2014 at 02:43:36PM -0700, Junio C Hamano wrote:
> > Kirill Smelkov <k...@mns.spb.ru> writes:
> > 
> > > instead of allocating it all the time for every subtree in
> > > __diff_tree_sha1, let's allocate it once in diff_tree_sha1, and then all
> > > callee just use it in stacking style, without memory allocations.
> > >
> > > This should be faster, and for me this change gives the following
> > > slight speedups for
> > >
> > >     git log --raw --no-abbrev --no-renames --format='%H'
> > >
> > >                 navy.git    linux.git v3.10..v3.11
> > >
> > >     before      0.618s      1.903s
> > >     after       0.611s      1.889s
> > >     speedup     1.1%        0.7%
> > >
> > > Signed-off-by: Kirill Smelkov <k...@mns.spb.ru>
> > > ---
> > >
> > > Changes since v1:
> > >
> > >  - don't need to touch diff.h, as the function we are changing became 
> > > static.
> > >
> > >  tree-diff.c | 36 ++++++++++++++++++------------------
> > >  1 file changed, 18 insertions(+), 18 deletions(-)
> > >
> > > diff --git a/tree-diff.c b/tree-diff.c
> > > index aea0297..c76821d 100644
> > > --- a/tree-diff.c
> > > +++ b/tree-diff.c
> > > @@ -115,7 +115,7 @@ static void show_path(struct strbuf *base, struct 
> > > diff_options *opt,
> > >   if (recurse) {
> > >           strbuf_addch(base, '/');
> > >           __diff_tree_sha1(t1 ? t1->entry.sha1 : NULL,
> > > -                          t2 ? t2->entry.sha1 : NULL, base->buf, opt);
> > > +                          t2 ? t2->entry.sha1 : NULL, base, opt);
> > >   }
> > >  
> > >   strbuf_setlen(base, old_baselen);
> > 
> > I was scratching my head for a while, after seeing that there does
> > not seem to be any *new* code added by this patch in order to
> > store-away the original length and restore the singleton base buffer
> > to the original length after using addch/addstr to extend it.
> > 
> > But I see that the code has already been prepared to do this
> > conversion.  I wonder why we didn't do this earlier ;-)
> 
> The conversion to reusing memory started in 48932677 "diff-tree: convert
> base+baselen to writable strbuf" which allowed to avoid "quite a bit of
> malloc() and memcpy()", but for this to work allocation at diff_tree()
> entry had to be there.
> 
> In particular it had to be there, because diff_tree() accepted base as C
> string, not strbuf, and since diff_tree() was calling itself
> recursively - oops - new allocation on every subtree.
> 
> I've opened the door for avoiding allocations via splitting diff_tree
> into high-level and low-level parts. The high-level part still accepts
> `char *base`, but low-level function operates on strbuf and recurses
> into low-level self.
> 
> The high-level diff_tree_sha1() still allocates memory for every
> diff(tree1,tree2), but that is significantly lower compared to
> allocating memory on every subtree...
> 
> The lesson here is: better use strbuf for api unless there is a reason
> not to.
> 
> 
> > Looks good.  Thanks.
> 
> Thanks.

Thanks again. Here it goes adjusted to __diff_tree_sha1 -> ll_diff_tree_sha1 
renaming:

(please keep author email)
---- 8< ----
From: Kirill Smelkov <k...@mns.spb.ru>
Date: Mon, 24 Feb 2014 20:21:48 +0400
Subject: [PATCH v3] tree-diff: reuse base str(buf) memory on sub-tree recursion

instead of allocating it all the time for every subtree in
ll_diff_tree_sha1, let's allocate it once in diff_tree_sha1, and then all
callee just use it in stacking style, without memory allocations.

This should be faster, and for me this change gives the following
slight speedups for

    git log --raw --no-abbrev --no-renames --format='%H'

                navy.git    linux.git v3.10..v3.11

    before      0.618s      1.903s
    after       0.611s      1.889s
    speedup     1.1%        0.7%

Signed-off-by: Kirill Smelkov <k...@mns.spb.ru>
---

Changes since v2:

 - adjust to __diff_tree_sha1 -> ll_diff_tree_sha1 renaming.

Changes since v1:

 - don't need to touch diff.h, as the function we are changing became
   static.

 tree-diff.c | 38 +++++++++++++++++++-------------------
 1 file changed, 19 insertions(+), 19 deletions(-)

diff --git a/tree-diff.c b/tree-diff.c
index 7fbb022..8c8bde6 100644
--- a/tree-diff.c
+++ b/tree-diff.c
@@ -8,7 +8,7 @@
 
 
 static int ll_diff_tree_sha1(const unsigned char *old, const unsigned char 
*new,
-                            const char *base_str, struct diff_options *opt);
+                            struct strbuf *base, struct diff_options *opt);
 
 /*
  * Compare two tree entries, taking into account only path/S_ISDIR(mode),
@@ -123,7 +123,7 @@ static void show_path(struct strbuf *base, struct 
diff_options *opt,
        if (recurse) {
                strbuf_addch(base, '/');
                ll_diff_tree_sha1(t1 ? t1->entry.sha1 : NULL,
-                                 t2 ? t2->entry.sha1 : NULL, base->buf, opt);
+                                 t2 ? t2->entry.sha1 : NULL, base, opt);
        }
 
        strbuf_setlen(base, old_baselen);
@@ -146,12 +146,10 @@ static void skip_uninteresting(struct tree_desc *t, 
struct strbuf *base,
 }
 
 static int ll_diff_tree_sha1(const unsigned char *old, const unsigned char 
*new,
-                            const char *base_str, struct diff_options *opt)
+                            struct strbuf *base, struct diff_options *opt)
 {
        struct tree_desc t1, t2;
        void *t1tree, *t2tree;
-       struct strbuf base;
-       int baselen = strlen(base_str);
 
        t1tree = fill_tree_descriptor(&t1, old);
        t2tree = fill_tree_descriptor(&t2, new);
@@ -159,17 +157,14 @@ static int ll_diff_tree_sha1(const unsigned char *old, 
const unsigned char *new,
        /* Enable recursion indefinitely */
        opt->pathspec.recursive = DIFF_OPT_TST(opt, RECURSIVE);
 
-       strbuf_init(&base, PATH_MAX);
-       strbuf_add(&base, base_str, baselen);
-
        for (;;) {
                int cmp;
 
                if (diff_can_quit_early(opt))
                        break;
                if (opt->pathspec.nr) {
-                       skip_uninteresting(&t1, &base, opt);
-                       skip_uninteresting(&t2, &base, opt);
+                       skip_uninteresting(&t1, base, opt);
+                       skip_uninteresting(&t2, base, opt);
                }
                if (!t1.size && !t2.size)
                        break;
@@ -181,7 +176,7 @@ static int ll_diff_tree_sha1(const unsigned char *old, 
const unsigned char *new,
                        if (DIFF_OPT_TST(opt, FIND_COPIES_HARDER) ||
                            hashcmp(t1.entry.sha1, t2.entry.sha1) ||
                            (t1.entry.mode != t2.entry.mode))
-                               show_path(&base, opt, &t1, &t2);
+                               show_path(base, opt, &t1, &t2);
 
                        update_tree_entry(&t1);
                        update_tree_entry(&t2);
@@ -189,18 +184,17 @@ static int ll_diff_tree_sha1(const unsigned char *old, 
const unsigned char *new,
 
                /* t1 < t2 */
                else if (cmp < 0) {
-                       show_path(&base, opt, &t1, /*t2=*/NULL);
+                       show_path(base, opt, &t1, /*t2=*/NULL);
                        update_tree_entry(&t1);
                }
 
                /* t1 > t2 */
                else {
-                       show_path(&base, opt, /*t1=*/NULL, &t2);
+                       show_path(base, opt, /*t1=*/NULL, &t2);
                        update_tree_entry(&t2);
                }
        }
 
-       strbuf_release(&base);
        free(t2tree);
        free(t1tree);
        return 0;
@@ -217,7 +211,7 @@ static inline int diff_might_be_rename(void)
                !DIFF_FILE_VALID(diff_queued_diff.queue[0]->one);
 }
 
-static void try_to_follow_renames(const unsigned char *old, const unsigned 
char *new, const char *base, struct diff_options *opt)
+static void try_to_follow_renames(const unsigned char *old, const unsigned 
char *new, struct strbuf *base, struct diff_options *opt)
 {
        struct diff_options diff_opts;
        struct diff_queue_struct *q = &diff_queued_diff;
@@ -314,13 +308,19 @@ static void try_to_follow_renames(const unsigned char 
*old, const unsigned char
        q->nr = 1;
 }
 
-int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const 
char *base, struct diff_options *opt)
+int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const 
char *base_str, struct diff_options *opt)
 {
+       struct strbuf base;
        int retval;
 
-       retval = ll_diff_tree_sha1(old, new, base, opt);
-       if (!*base && DIFF_OPT_TST(opt, FOLLOW_RENAMES) && 
diff_might_be_rename())
-               try_to_follow_renames(old, new, base, opt);
+       strbuf_init(&base, PATH_MAX);
+       strbuf_addstr(&base, base_str);
+
+       retval = ll_diff_tree_sha1(old, new, &base, opt);
+       if (!*base_str && DIFF_OPT_TST(opt, FOLLOW_RENAMES) && 
diff_might_be_rename())
+               try_to_follow_renames(old, new, &base, opt);
+
+       strbuf_release(&base);
 
        return retval;
 }
-- 
1.9.rc0.143.g6fd479e
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