Messages in this thread | | | Date | Sun, 13 Jul 2008 00:07:03 -0700 | From | Andrew Morton <> | Subject | Re: Runtime accounting bug? |
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On Sun, 6 Jul 2008 14:00:22 -0400 (EDT) George Glover <hyperborean@comcast.net> wrote:
> Hello, > > I run two copies (dual processor system) of "mprime" from the GIMPS > project. After a while running (weeks?) the cumulative runtime reported by > top increments faster than real time, then after a while (unknown how long) > the value increments normally again. Then, maybe something overflows - but > runtime accounting stops entirely even though the process is in the run state. > > (mprime is a cpu-bound low priority process like seti@home and friends.) > > I presently have a stuck process and a one that should soon start to > increment faster than possible. > > I have verified that the "stuck" process is indeed running since it continues > to generate output. > > Here is the "stuck" process: > > cat /proc/4126/stat; sleep 5; cat /proc/4126/stat > 4126 (mprime) R 2984 4126 2984 34819 4126 4202496 16530 0 4 0 2124505930 661087 0 0 39 19 1 0 8442861 21483520 3733 4294967295 134512640 138881564 3220348480 3220345732 135248565 0 0 0 16386 0 0 0 17 1 0 0 0 0 0 ^^^^^^^^^^ > 4126 (mprime) R 2984 4126 2984 34819 4126 4202496 16530 0 4 0 2124505930 661087 0 0 39 19 1 0 8442861 21483520 3733 4294967295 134512640 138881564 3220348480 3220345736 135241038 0 0 0 16386 0 0 0 17 1 0 0 0 0 0 ^^^^^^^^^^
yes? The 14th column, do_task_stat()'s cputime_to_clock_t(utime)?
> > > Here is the other process started more recently: > > cat /proc/18312/stat; sleep 5; cat /proc/18312/stat > 18312 (mprime) R 2969 18312 2969 34818 18312 4202496 7657 0 1 0 140549087 660363 0 0 39 19 1 0 346388363 35483648 7152 4294967295 134512640 138881564 3221166480 3221163732 135246526 0 0 0 16386 0 0 0 17 1 0 0 0 0 0 ^^^^^^^^^ > 18312 (mprime) R 2969 18312 2969 34818 18312 4202496 7657 0 1 0 140549510 660364 0 0 39 19 1 0 346388363 35483648 7152 4294967295 134512640 138881564 3221166480 3221163740 135280398 0 0 0 16386 0 0 0 17 1 0 0 0 0 0 ^^^^^^^^^
Here it changed.
> > > Top output sorted by cpu time: > > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ TIME COMMAND > 4126 zed 39 19 20980 14m 968 R 0 0.4 354194:30 5903h mprime > 18312 zed 39 19 34652 27m 952 R 84 0.8 23544:49 392,24 mprime > > > uptime: > 12:50:47 up 60 days, 18:58, 25 users, load average: 2.20, 2.21, 2.26 > > cat /proc/version > Linux version 2.6.25.1 (root@(none)) (gcc version 4.1.2) #3 SMP PREEMPT Tue > May 6 01:53:17 EDT 2008 > > The machine is a dual processor 1.2Ghz Athlon MP system. It's generally > problem free with maybe 1 bit error a year reported from the ecc ram. > > As the problem takes so long to repeat I do not know how to approach it. > It has also been present for the past few kernels, since 2.6.23 if I > recall. > > Anyone have any thoughts? It seems more cosmetic than critical. >
My suspicion wold be that some of the arithmetic in here:
static cputime_t task_utime(struct task_struct *p) { clock_t utime = cputime_to_clock_t(p->utime), total = utime + cputime_to_clock_t(p->stime); u64 temp;
/* * Use CFS's precise accounting: */ temp = (u64)nsec_to_clock_t(p->se.sum_exec_runtime);
if (total) { temp *= utime; do_div(temp, total); } utime = (clock_t)temp;
p->prev_utime = max(p->prev_utime, clock_t_to_cputime(utime)); return p->prev_utime; }
is suffering overflows at very high values of p->utime.
It's a 32bit machine, yes?
It would useful to know what your values of TICK_NSEC, NSEC_PER_SEC and USER_HZ are.
Peter, you recently fixed some of that time conversion arithmetic? But I think those fixes made it into 2.6.25?
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