On Thu, 14 Aug 2008, Linus Torvalds wrote: > Btw, it's not that hard to run oprofile (link git statically to get better > numbers). For me, the answer to what is going on for a kernel rev-list is > pretty straightforward: > > 263742 26.6009 lookup_object > 135945 13.7113 inflate > 110525 11.1475 inflate_fast > 75124 7.5770 inflate_table > 64676 6.5232 strlen > 48635 4.9053 memcpy > 47744 4.8154 find_pack_entry_one > 35265 3.5568 _int_malloc > 31579 3.1850 decode_tree_entry > 28388 2.8632 adler32 > 19441 1.9608 process_tree > 10398 1.0487 patch_delta > 8925 0.9002 _int_free > .. OK, inflate went down since last time I profiled this, but that's probably because lookup_object went up. > so most of it is in inflate, Which, again, would be eliminated entirely by pack v4. > but I suspect the cost of "lookup_object()" > is so high becuase when we parse the trees we also have to look up every > blob - even if they didn't change - just to see whether we already saw it > or not. One optimization with pack v4 was to have delta chunks aligned on tree records, and because tree objects are no longer compressed, parsing a tree object could be done by simply walking the delta chain directly. Then, another optimization would consist of simply skipping any part of a tree object making a delta reference to a base object which has already been parsed which would avoid a large bunch of lookup_object() calls too. And because delta base objects are normally seen first in recency order then this would reduce the combinatorial complexity significantly. Nicolas -- 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
