Jeff King <peff@xxxxxxxx> writes: > On Thu, Aug 11, 2016 at 12:13:09PM -0400, Jeff King wrote: > >> Here are the numbers for linux.git: >> >> depth | size | % | rev-list | % | log -Sfoo | % >> -------+-------+-------+----------+--------+-----------+------- >> 250 | 967MB | n/a | 48.159s | n/a | 378.088 | n/a >> 100 | 971MB | +0.4% | 41.471s | -13.9% | 342.060 | -9.5% >> 50 | 979MB | +1.2% | 37.778s | -21.6% | 311.040s | -17.7% >> 10 | 1.1GB | +6.6% | 32.518s | -32.5% | 279.890s | -25.9% >> [...] >> >> You can see that that the CPU savings for regular operations improves as we >> decrease the depth. The savings are less for "rev-list" on a smaller repository >> than they are for blob-accessing operations, or even rev-list on a larger >> repository. This may mean that a larger delta cache would help (though setting >> core.deltaBaseCacheLimit by itself doesn't). > > The problem with deltaBaseCacheLimit is that it only changes the memory > parameter, but there are a fixed number of slots in the data structure. > Bumping it like this: > > diff --git a/sha1_file.c b/sha1_file.c > index 02940f1..ca79703 100644 > --- a/sha1_file.c > +++ b/sha1_file.c > @@ -2073,7 +2073,7 @@ static void *unpack_compressed_entry(struct packed_git *p, > return buffer; > } > > -#define MAX_DELTA_CACHE (256) > +#define MAX_DELTA_CACHE (1024) > > static size_t delta_base_cached; > > along with the cache size does help (this was discussed a year or two > ago, but nobody ever followed up with numbers or patches). Yeah, and I also think Linus's "--depth=250 is just a sample; it will not perform well" already cited the number of delta-cache entries being the limiting factor. > I don't think bumping MAX_DELTA_CACHE naively is a good idea, though. I > seem to recall that it has scaling problems as it grows, so we may want > a better data structure (but I haven't looked at it recently enough to > say anything intelligent). Me neither. In any case, I do think reducing the aggressive depth down to 50 is a very sensible move. I also suspect that window size may want to be a bit increased (or even made dynamic; the first time we need the window size determined is after to_pack.objects[] array is fully populated, so we could use the number of commits as one of the hint, for example), but that can be treated as a separate topic. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html