On Thu, 18 Nov 2010 18:27:06 +1100 Dave Chinner <david@xxxxxxxxxxxxx> wrote: > > > Indeed, nobody has > > > realised (until now) just how inefficient it really is because of > > > the fact that the overhead is mostly hidden in user process system > > > time. > > > > "hidden"? You do "time dd" and look at the output! > > > > _now_ it's hidden. You do "time dd" and whee, no system time! > > What I meant is that the cost of foreground writeback was hidden in > the process system time. Now we have separated the two of them, we > can see exactly how much it was costing us because it is no longer > hidden inside the process system time. About a billion years ago I wrote the "cyclesoak" thingy which measures CPU utilisation the other way around: run a lowest-priority process on each CPU in the background, while running your workload, then find out how much CPU time cyclesoak *didn't* consume. That way you account for everything: user time, system time, kernel threads, interrupts, softirqs, etc. It turned out to be pretty accurate, despite the then-absence of SCHED_IDLE. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>