Hello Balbir, On Tuesday 16 October 2007, Balbir Singh wrote: > Christian Borntraeger wrote: > > Am Dienstag, 16. Oktober 2007 schrieb Balbir Singh: > >> I am trying to think out loud as to what the root cause of the problem > >> might be. In one of the discussion threads, I saw utime going > >> backwards, which seemed very odd, I suspect that those are rounding > >> errors. > >> > >> I don't understand your explanation below > >> > >> Initially utime = 9, stime = 0, sum_exec_runtime = S1 > >> > >> Later > >> > >> utime = 9, stime = 1, sum_exec_runtime = S2 > >> > >> We can be sure that S >= (utime + stime) > > > > I think here is the problem. How can we be sure? We cant. utime and > > stime are sampled, so they can be largely off in any direction,if the > > program sleeps often and manages to synchronize itself to the timer > > tick. Lets say a program only does a simple system call and then > > sleeps. So sum_exec_runtime is increased by lets say 1000 cycles on a > > 1Ghz box which means 1000ns. If now the timer tick happens exactly at > > this moment, stime is increased by 1 tick = 1000000ns. > > Yes, I thought of that just after I sent out my email. In the case that > you mention, the utime and stime accounting is incorrect anyway :-) > I think we need to find a better solution. I was going to propose that > we round correctly in (the divisions in) > > 1. task_utime() > 2. clock_t_to_cputime() > > I suspect we'll need to round task_utime() to p->utime if the value of > task_utime() < p->utime and the same thing for task_stime(). I've tried > reproducing the problem on my UML setup without any success. Let me > try and grab an x86 box.
Any progress on this issue? I noticed that it's still there in current git. If a better implementation is not expected any time soon, how about an ACK on the reversion patch Christian proposed in http://lkml.org/lkml/2007/10/16/76 so we can at least get rid of the regression? Thanks, Frans Pop - 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/
