* Martin Schwidefsky <schwidefsky@xxxxxxxxxx> [2010-09-27 15:42:57]: > On Sun, 26 Sep 2010 20:11:27 +0200 > Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > > > Hi, > > > > On 09/24, Michael Holzheu wrote: > > > > > > On Thu, 2010-09-23 at 19:10 +0200, Oleg Nesterov wrote: > > > > > > > > On 09/23, Michael Holzheu wrote: > > > > > > > > > > Currently there are code pathes (e.g. for kthreads) where the consumed > > > > > CPU time is not accounted to the parents cumulative counters. > > > > > > > > Could you explain more? > > > > > > I think one place was "khelper" (kmod.c). It is created with > > > kernel_thread() and it exits without having accounted the times with > > > sys_wait() to the parent's ctimes > > > > No. Well yes, it is not accounted, but this is not because it is > > kthread. > > We noticed that behavior with kernel threads but as you point out > the problem is bigger than that. > > > To simplify the discussion, lets talk about utime/cutime only, > > and lets forget about the multithreading. > > > > It is very simple, currently linux accounts the exiting task's > > utime and adds its to ->cutime _only_ if parent does do_wait(). > > If parent ignores SIGCHLD, the child reaps itself and it is not > > accounted. > > > > I do not know why it was done this way, but I'm afraid we can't > > change this historical behaviour. > > Why? I would consider it to be a BUG() that the time is not accounted. > Independent of the fact that a parent wants to see the SIGCHLD and > the exit status of its child the process time of the child should be > accounted, no? And I'm not a particular fan of the "this has always > been that way" reasoning. > > > > Ok, the problem is that I did not consider exiting threads that are no > > > thread group leaders. When they exit the ctime of the parent is not > > > updated. Instead the time is accumulated in the signal struct. > > > > I think I am a bit confused, but see above. With or without threads > > the whole process can exit without accounting. > > Got the part about self-reaping processes. But there is another issue: > consider an exiting thread where the group leader is still active. > The time for the thread will be added to the utime/stime fields in > the signal structure. Taskstats will happily ignore that time while > the group leader is still running. > Why do you say that? Not sure your comment is very clean, in fill_tgid, we do 1. Accumulate signal stats (contains stats for dead threads) 2. Accumulate stats for current threads fill_tgid_exit does something similar > Please keep in mind that we want to get to a point where it is > possible to get a 100% coverage of cpu cycles in the last snapshot > cycle through the taskstats interface. Otherwise the precise top > would not be very precise .. -- Three Cheers, Balbir -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
