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Re: [PATCH] FSFS speedup (was: Re: Making blame even faster)

From: Greg Hudson <ghudson_at_MIT.EDU>
Date: 2005-02-26 18:43:38 CET

On Tue, 2005-02-22 at 20:24, Daniel Berlin wrote:
> On Mon, 2005-02-21 at 23:03 -0500, Greg Hudson wrote:
> > On Mon, 2005-02-21 at 20:37, Daniel Berlin wrote:
> > > ChangeLog is > SVN_DELTA_WINDOW_SIZE when deltified, and you only
> > > auto-expand the first window
> >
> > That doesn't agree with my reading of Peter's change. It looks like he
> > auto-expands all windows of the last rep.
> >
> > (Something is obviously wrong, but I'm not convinced this is it.)
> Fair enough.
> I've put the repo in question (it's about 1/8th the total revisions of
> our changelog) at http://www.toolchain.org/~dberlin/repo.dump.bz2

As far as I can tell, what's wrong is the basic premise of this whole
optimization. A chain of deltas with no "copy from target" operations
does not necessarily avoid copy_source_ops().

(This is from loading your sample repository and poking around in gdb
with a checkout of the head of ChangeLog. I see copy_source_ops()
activity from the very first window composition. window_B of this
composition comes from rev 4550 and has only four instructions, none of
which are "copy from target" instructions.)

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Received on Sat Feb 26 18:45:03 2005

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