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diff: cache textconv output

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Running a textconv filter can take a long time. It's
particularly bad for a large file which needs to be spooled
to disk, but even for small files, the fork+exec overhead
can add up for something like "git log -p".

This patch uses the notes-cache mechanism to keep a fast
cache of textconv output. Caches are stored in
refs/notes/textconv/$x, where $x is the userdiff driver
defined in gitattributes.

Caching is enabled only if diff.$x.cachetextconv is true.

In my test repo, on a commit with 45 jpg and avi files
changed and a textconv to show their exif tags:

  [before]
  $ time git show >/dev/null
  real    0m13.724s
  user    0m12.057s
  sys     0m1.624s

  [after, first run]
  $ git config diff.mfo.cachetextconv true
  $ time git show >/dev/null
  real    0m14.252s
  user    0m12.197s
  sys     0m1.800s

  [after, subsequent runs]
  $ time git show >/dev/null
  real    0m0.352s
  user    0m0.148s
  sys     0m0.200s

So for a slight (3.8%) cost on the first run, we achieve an
almost 40x speed up on subsequent runs.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King
2010-04-01 20:12:15 -04:00
committed by Junio C Hamano
parent 840383b2c2
commit d9bae1a178
5 changed files with 185 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files

52
diff.c
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@ -43,7 +43,7 @@ static char diff_colors[][COLOR_MAXLEN] = {
};
static void diff_filespec_load_driver(struct diff_filespec *one);
static size_t fill_textconv(const char *cmd,
static size_t fill_textconv(struct userdiff_driver *driver,
struct diff_filespec *df, char **outbuf);
static int parse_diff_color_slot(const char *var, int ofs)
@ -466,8 +466,8 @@ static void emit_rewrite_diff(const char *name_a,
const char *name_b,
struct diff_filespec *one,
struct diff_filespec *two,
const char *textconv_one,
const char *textconv_two,
struct userdiff_driver *textconv_one,
struct userdiff_driver *textconv_two,
struct diff_options *o)
{
int lc_a, lc_b;
@ -1569,14 +1569,26 @@ void diff_set_mnemonic_prefix(struct diff_options *options, const char *a, const
options->b_prefix = b;
}
static const char *get_textconv(struct diff_filespec *one)
static struct userdiff_driver *get_textconv(struct diff_filespec *one)
{
if (!DIFF_FILE_VALID(one))
return NULL;
if (!S_ISREG(one->mode))
return NULL;
diff_filespec_load_driver(one);
return one->driver->textconv;
if (!one->driver->textconv)
return NULL;
if (one->driver->textconv_want_cache && !one->driver->textconv_cache) {
struct notes_cache *c = xmalloc(sizeof(*c));
struct strbuf name = STRBUF_INIT;
strbuf_addf(&name, "textconv/%s", one->driver->name);
notes_cache_init(c, name.buf, one->driver->textconv);
one->driver->textconv_cache = c;
}
return one->driver;
}
static void builtin_diff(const char *name_a,
@ -1593,7 +1605,8 @@ static void builtin_diff(const char *name_a,
const char *set = diff_get_color_opt(o, DIFF_METAINFO);
const char *reset = diff_get_color_opt(o, DIFF_RESET);
const char *a_prefix, *b_prefix;
const char *textconv_one = NULL, *textconv_two = NULL;
struct userdiff_driver *textconv_one = NULL;
struct userdiff_driver *textconv_two = NULL;
struct strbuf header = STRBUF_INIT;
if (DIFF_OPT_TST(o, SUBMODULE_LOG) &&
@ -3888,13 +3901,13 @@ static char *run_textconv(const char *pgm, struct diff_filespec *spec,
return strbuf_detach(&buf, outsize);
}
static size_t fill_textconv(const char *cmd,
static size_t fill_textconv(struct userdiff_driver *driver,
struct diff_filespec *df,
char **outbuf)
{
size_t size;
if (!cmd) {
if (!driver || !driver->textconv) {
if (!DIFF_FILE_VALID(df)) {
*outbuf = "";
return 0;
@ -3905,8 +3918,29 @@ static size_t fill_textconv(const char *cmd,
return df->size;
}
*outbuf = run_textconv(cmd, df, &size);
if (driver->textconv_cache) {
*outbuf = notes_cache_get(driver->textconv_cache, df->sha1,
&size);
if (*outbuf)
return size;
}
*outbuf = run_textconv(driver->textconv, df, &size);
if (!*outbuf)
die("unable to read files to diff");
if (driver->textconv_cache) {
/* ignore errors, as we might be in a readonly repository */
notes_cache_put(driver->textconv_cache, df->sha1, *outbuf,
size);
/*
* we could save up changes and flush them all at the end,
* but we would need an extra call after all diffing is done.
* Since generating a cache entry is the slow path anyway,
* this extra overhead probably isn't a big deal.
*/
notes_cache_write(driver->textconv_cache);
}
return size;
}