QMD Checkpoints

[ChasR]

Today, I discovered an error in a bit of data I've been spouting about at times, QMD checkpoints. A couple of months ago, I noticed frame time varying on QMDs by 46 seconds every 4 frames or so. The only difference I saw at the time was that every fourth frame had a checkpoint in it. I assumed that since the rig I was looking at was folding almost exactly 15:00 per frame that sometimes a checkpoint was triggered and sometimes not. What I later learned was that there aren't the same number of steps per frame in a QMD. They vary from 20 to 22 steps, after convergence, depending on the total number of steps in the QMD. If a frame with 20 steps completes in 15:00 a frame with 21 steps will take 45 seconds longer. On the rig I was looking at, the extra step took the frame past the checkpoint time. The difference which I reported at 46 seconds was actually the extra step plus the checkpoint time.

I recalculated the checkpoint time today and find that one checkpoint per frame adds about 2 seconds per frame on sig rig #2 or 3:20 per WU. In comparison to the 600 pointers, which take about 8-9 seconds, QMD checkpoints are actually pretty quick. The slower the HD, the longer the checkpoint will take so your mileage may vary.

[TollhouseFrank]

hmm... so should checkpoints for QMD machines be set to say 17 or so minutes to account for convergance, or did i misread what you posted?

[ChasR]

I usually set checkpoints to 30 on rigs folding 24/7. However, If you're folding WUs that take 32 minutes per frame you're going to have to have one checkpoint/frame no matter what so it may as well be set at 17 minutes. You'll lose much less work on average on power failure or shutdown. I think it's a complete waste to write a checkpoint just before completion of a frame when another checkpoint is written anyway.
On QMDs preconvergence frames are faster than post convergence. I try to avoid writting any checkpoints other than those written at frame completion. If you set it longer than the longest observed frame time you'll acomplish that. But my real point is that the checkpoints din't add all that much time on QMDs, 2 seconds per checkpoint

[TollhouseFrank]

so you are lookin' at what... 20 seconds over the life of a QMD?

[ChasR]

200. 3 minutes 20 seconds, if you have one checkpoint per frame. If you checkpoint at something ridiculous like 3 minutes, you'll add a lot more.