On 5 May 2015 at 16:38, David du Colombier <0in...@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.
