Windows performance / threading file access

[Stefan Zager <szager@google.com>]

Hi folks,

I don't follow the mailing list carefully, so forgive me if this has
been discussed before, but:

I've noticed that when working with a very large repository using msys
git, the initial checkout of a cloned repository is excruciatingly
slow (80%+ of total clone time).  The root cause, I think, is that git
does all the file access serially, and that's really slow on Windows.

Has anyone considered threading file access to speed this up?  In
particular, I've got my eye on this loop in unpack-trees.c:

static struct checkout state;
static int check_updates(struct unpack_trees_options *o)
{
        unsigned cnt = 0, total = 0;
        struct progress *progress = NULL;
        struct index_state *index = &o->result;
        int i;
        int errs = 0;

        ...

        for (i = 0; i < index->cache_nr; i++) {
                struct cache_entry *ce = index->cache[i];

                if (ce->ce_flags & CE_UPDATE) {
                        display_progress(progress, ++cnt);
                        ce->ce_flags &= ~CE_UPDATE;
                        if (o->update && !o->dry_run) {
                                errs |= checkout_entry(ce, &state, NULL);
                        }
                }
        }
        stop_progress(&progress);
        if (o->update)
                git_attr_set_direction(GIT_ATTR_CHECKIN, NULL);
        return errs != 0;
}


Any thoughts on adding threading around the call to checkout_entry?


Thanks in advance,

Stefan