Re: [PATCH 2/2] pack-objects: fix threaded load balancing

[Nicolas Pitre <nico@cam.org>]

On Mon, 10 Dec 2007, Jon Smirl wrote:

> It seems to be caused by looping over those runs of 100,000 identical
> hash entries.

As mentioned earlier, there simply can't be 100000 identical hash 
entries.

> 5091699 24.6407 :                       for (entry = index->hash[i]; entry < index->hash[i+1]; entry++) {
> 5301791 25.6575 :                               const unsigned char *ref = entry->ptr;

This loop is the very heart of the delta search code.  It is normal to 
see it high on the graph.  In some worst cases, this loop might even be 
entered for every byte in the source buffer.

And yet I bring you back to your observation about the fact that the 
source pack used for the repack (whether it is the 2.1GB pack or the 
300MB pack) has a great influence on the performance outcome.  The code 
above, though, would be executed the very exact number of times, and the 
exact amount of memory allocated, regardless of the source pack used (as 
long as you use -f with 'git repack' of course).

So this cannot be the culprit.


Nicolas