Hello Nikola, On Fri, Apr 29, 2011 at 12:02:00PM +0200, Nikola Ciprich wrote: > (another CC added) > > Hello Willy! > > I made some statistics of our servers regarding kernel version and uptime. > Here are some my thoughts: > - I'm 100% sure this problem wasn't present in kernels <= 2.6.30.x (we've got > a lot of boxes with uptimes >600days) > - I'm 90% sure this problem also wasn't present in 2.6.32.16 (we've got 6 > boxes running for 235 to 280days)
OK those are all precious information. > What I'm not sure is, whether this is present in 2.6.19, I have: > 2 boxes running 2.6.32.19 for 238days and one 2.6.32.20 for 216days. > I also have a bunch ov 2.6.32.23 boxes, which are now getting close to > 200days uptime. > But I suspect this really is first problematic version, more on it later. > First regarding Your question about CONFIG_HZ - we use 250HZ setting, which > leads me to following: > 250 * 60 * 60 * 24 * 199 = 4298400000 which is value a little over 2**32! So > maybe some unsingned long variable > might overflow? Does this make sense? Yes of course it makes sense, that was also my worries. 2^32 jiffies at 250 Hz is slightly less than 199 days. Maybe an overflow somewhere keeps propagating wrong results on some computations. I remember having encountered a lot of funny things when trying to get 2.4 get past the 497 days limit using the jiffies64 patch. So I would not be surprized at all that we're in a similar situation here. Also, I've checked the Debian kernel config where we had the divide overflow and it was running at 250 Hz too. > And to my suspicion about 2.6.32.19, there is one commit which maybe is > related: > > commit 0cf55e1ec08bb5a22e068309e2d8ba1180ab4239 > Author: Hidetoshi Seto <[email protected]> > Date: Wed Dec 2 17:28:07 2009 +0900 > > sched, cputime: Introduce thread_group_times() > > This is a real fix for problem of utime/stime values decreasing > described in the thread: > > http://lkml.org/lkml/2009/11/3/522 > > Now cputime is accounted in the following way: > > - {u,s}time in task_struct are increased every time when the thread > is interrupted by a tick (timer interrupt). > > - When a thread exits, its {u,s}time are added to signal->{u,s}time, > after adjusted by task_times(). > > - When all threads in a thread_group exits, accumulated {u,s}time > (and also c{u,s}time) in signal struct are added to c{u,s}time > in signal struct of the group's parent. > . > . > . > > I haven't studied this into detail yet, but it seems to me it might really be > related. Hidetoshi-san - do You have some opinion about this? > Could this somehow either create or invoke the problem with overflow of some > variable which would lead to division by zero or similar problems? > > Any other thoughts? There was a kernel parameter in the past that was used to make jiffies wrap a few minutes after boot, maybe we should revive it to try to reproduce without waiting 7 new months :-/ Last, the "advantage" with a suspected regression in a stable series is that there are a lot less patches to test. Regards, Willy _______________________________________________ stable mailing list [email protected] http://linux.kernel.org/mailman/listinfo/stable
