[PATCH 6/7] pack-objects: allow for early delta deflating
- From
Nicolas Pitre <nico@cam.org>
- Date
- May 2, 2008, 19:11 UTC
- Message-ID
- <1209755511-7840-7-git-send-email-nico@cam.org>
- In-Reply-To
- <1209755511-7840-6-git-send-email-nico@cam.org>
When the delta data is cached in memory until it is written to a pack file on disk, it is best to compress it right away in find_deltas() for the following reasons:
- we have to compress that data anyway;
- this allows for caching more deltas with the same cache size limit;
- compression is potentially threaded.
This last point is especially relevant for SMP run time. For example, repacking the Linux repo on a quad core processor using 4 threads with all default settings produce the following results before this change:
real 2m27.929s user 4m36.492s sys 0m3.091s
And with this change applied:
real 2m13.787s user 4m37.486s sys 0m3.159s
So the actual execution time stayed more or less the same but the wall clock time is shorter.
This is however not a good thing to do when generating a pack for network transmission. In that case, the network is most likely to throttle the data throughput, so it is best to make find_deltas() faster in order to start writing data ASAP since we can afford spending more time between writes to compress the data at that point.
Signed-off-by: Nicolas Pitre <nico@cam.org> --- builtin-pack-objects.c | 35 ++++++++++++++++++++++++++++++++++- 1 files changed, 34 insertions(+), 1 deletions(-)
diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c index 4319e7b..f5dcd20 100644 --- a/builtin-pack-objects.c +++ b/builtin-pack-objects.c @@ -43,6 +43,7 @@ struct object_entry { */ void *delta_data; /* cached delta (uncompressed) */ unsigned long delta_size; /* delta data size (uncompressed) */ + unsigned long z_delta_size; /* delta data size (compressed) */ unsigned int hash; /* name hint hash */ enum object_type type; enum object_type in_pack_type; /* could be delta */ @@ -301,6 +302,11 @@ static unsigned long write_object(struct sha1file *f, buf = read_sha1_file(entry->idx.sha1, &type, &size); if (!buf) die("unable to read %s", sha1_to_hex(entry->idx.sha1)); + /* make sure no cached delta data remains from a + previous attempt before a pack split occured */ + free(entry->delta_data); + entry->delta_data = NULL; + entry->z_delta_size = 0; } else if (entry->delta_data) { size = entry->delta_size; buf = entry->delta_data; @@ -313,7 +319,11 @@ static unsigned long write_object(struct sha1file *f, type = (allow_ofs_delta && entry->delta->idx.offset) ? OBJ_OFS_DELTA : OBJ_REF_DELTA; } - datalen = do_compress(&buf, size); + + if (entry->z_delta_size) + datalen = entry->z_delta_size; + else + datalen = do_compress(&buf, size); /* * The object header is a byte of 'type' followed by zero or @@ -1447,6 +1457,29 @@ static void find_deltas(struct object_entry **list, unsigned *list_size, best_base = other_idx; } + /* + * If we decided to cache the delta data, then it is best + * to compress it right away. First because we have to do + * it anyway, and doing it here while we're threaded will + * save a lot of time in the non threaded write phase, + * as well as allow for caching more deltas within + * the same cache size limit. + * ... + * But only if not writing to stdout, since in that case + * the network is most likely throttling writes anyway, + * and therefore it is best to go to the write phase ASAP + * instead, as we can afford spending more time compressing + * between writes at that moment. + */ + if (entry->delta_data && !pack_to_stdout) { + entry->z_delta_size = do_compress(&entry->delta_data, + entry->delta_size); + cache_lock(); + delta_cache_size -= entry->delta_size; + delta_cache_size += entry->z_delta_size; + cache_unlock(); + } + /* if we made n a delta, and if n is already at max * depth, leaving it in the window is pointless. we * should evict it first.
-- 1.5.5.1.226.g6f6e8