(please CC me) I am copying a large file +-1GB to another machine using scp, this was the easiest way to reproduce.
I've done this a few dozen times, and there's few odd things about this: sometimes i have read speeds of around 20MB/s, at that time, the CPU is about 60% idle and max 10% io wait. but mostly, i have read speeds around 5MB/s, and CPU is 0% idle and 70% io waiting. This is a little odd, but one could argue that there are lots of factors, etc... True, however, i should note that, allthough i ran the tests immediately after each other; that if i had low IO wait less than 10%, it stayed that way, until the file was completely copied. AND if i had IO wait higher than 50%, it also stayed that way until the file was copied; immediately after all copies, there is no IO wait. even when no other process is writing for several seconds, this continues. same things with the speeds, either i have a consistent 5MB/s read, or 20MB/s read; never in between or fluctuating. I've tried to eliminate lots of other possibilities, by doing cat /path/to/file >/dev/null ; to just do the IO reading; usually this makes a extremely high io waiting (around 90%), but the read speeds are the same, either around 5 or around 20. stats are observed through iostat and mpstat. (in slow or normal case: iostat -x gives sda total usage 100%) I would like to trace this io wait to what process and device (I'm fairly sure it's the process i'm testing this with (eg: scp or cat)). but i don't know such a utility to find it. I've tried to google on this, but allthough there is lots of stuff with high IO wait in it. no solutions seems to be present. now, i can accept that sometimes, it's just slow. but the inconsistency is too consistent to be normal. can anyone give me some constructive info/help on this? thanks in advance -- AL13N is my name and head-biting is my game. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
