* Damien Wyart <damien.wyart@xxxxxxx> wrote: > > > So I followed the tracing steps in the tutorial (with the 1 sec sleep), > > > which gave me this: > > > http://damien.wyart.free.fr/trace_2.6.29-rc5_ksoftirqd_prob.txt.gz > > > thanks. There's definitely some weirdness visible in the trace, > > for example: > > > 0) gpm-1879 => ksoftir-4 > > ------------------------------------------ > > > 0) 0.964 us | finish_task_switch(); > > 0) ! 1768184 us | } > > 0) | do_softirq() { > > 0) | __do_softirq() { > > 0) | rcu_process_callbacks() { > > > the 1.7 seconds 'overhead' there must be a fluke - you'd notice it if > > ksoftirqd _really_ took that much time to execute. > > > One possibility for these symptoms would be broken scheduler timestamps. > > Could you enable absolute timestamp printing via: > > > echo funcgraph-abstime > trace_options > > Mmm, seems I do not have this option recognized in rc5, so could not > test. Will retry all this with tip tomorrow... Yeah, it got renamed in -tip - in rc5 it's iter_ctrl. > > Also, my guess is that if you boot via idle=poll, the symptoms go away. > > This would strengthen the suspicion that it's scheduler-clock troubles. > > In fact, with idle=poll, the symptoms do not go away, they are much > stronger: without it, ksotirqd have a few % of CPU in top output; with > it, they have 20 or 30% and the global average is not far from 1. > > On my laptop (I do not have it at hand today), with rc3-gitX (did not > retest with rc5), the load avg was ok, but I saw that after boot, > ksoftird threads had a quite higher running time in top than with > 2.6.28. I am surprised nobody reported this yet... > > I attach to this mail config and dmesg if needed (this is rc5 without > idle=poll). > > If a trace with funcgraph-abstime is interesting for you with tip, > I will do this tomorrow. Yes, an abstime trace would be useful. > checking TSC synchronization [CPU#0 -> CPU#1]: passed. > Switched to high resolution mode on CPU 1 Lets double-check your scheduler clock first. Without being able to trust the clock we cannot trust the task stats nor the trace output. What does this check display: http://people.redhat.com/mingo/time-warp-test/time-warp-test.c Does it find any TSC time warps? Also, could you send the output of: http://people.redhat.com/mingo/cfs-scheduler/tools/cfs-debug-info.sh Run it while you can see the ksoftirqd anomaly. Ingo -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
