On 5 May 2015 at 16:38, David du Colombier <0intro@gmail.com> wrote:

> > How many times do you time it on each machine?
>
> Maybe ten times. The results are always the same ~5%.
> Also, I restarted vacfs between each try.


It was the effect of the ram caches that prompted the question.

My experience is similar to Steve's: it was faster, and now it's initially
very very slow.
I looked at changes from that version of venti to this, and I didn't see
anything that would cause that.
(The problem could be outside venti, but I looked at some possibly relevant
kernel changes too.)

Note that the raw drive speed on my venti machine is fine (no doubt it
could be better, but it's fine).
I convinced myself through experiments that the problem was with venti, not
fossil.
I used some debugging code in venti and had the impression that it took a
surprisingly long time
to handle each request: that the time was in venti. The effect was similar
to that of a lost
interrupt for a device driver. I used ratrace on it, but didn't spot an
obvious culprit.
I was tempted to rip out or disable the drive scheduling code in venti to
see what happened, but
not for the first time I ran out of time and had to get back to some other
work.

One thing I didn't know was that the results were different when fossil was
on a different machine.
I thought I'd tried that with vacfs myself, but apparently not or mine was
as slow as when on the same
machine.