On Mon, 30 Mar 2009, Linus Torvalds wrote:
>
> This if anything makes things just go slower.
>
> Not much, but some. It went from 36.566s to 38.070s. That may be in the
> noise, I've not done any sensitivity analysis.
>
> I thought you perhaps had a missing "parse_commit()" making the
> reachability thing not work (look_up_gently parses the object, but if it's
> a tag deref_tag() will dereference it until it hits a commit, but never
> parse the commit). But that wasn't it.
Ahhah.
I know why it makes things slower.
The slow case is already inside that whole:
if (timestamp < cb->cmd->expire_unreachable) {
if-statement, so the thing that slows down is if we hit a commit that is
_older_ than the expire limit.
But your whole "mark_reachable()" thing only marks things _younger_ than
that reachable. So you mark exactly the wrong things reachable - you mark
the ones that we don't even care about.
If I do
mark_reachable(cb.ref_commit, 0);
instead (to traverse the _whole_ tree, with no regards to date), the time
shrinks to 1.7s. But of course, that's also wrong.
Qutie frankly, I don't really understand why the logic isn't just
if (timestamp < cb->cmd->expire_unreachable)
goto prune;
why is that reachability so important?
Linus
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