Messages in this thread | | | Date | Mon, 5 Jan 2009 15:54:29 -0600 | From | Dimitri Sivanich <> | Subject | Re: 2.6.27.8 scheduler bug - threads not being scheduled for long periods |
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On Mon, Jan 05, 2009 at 09:55:58PM +0100, Peter Zijlstra wrote: > On Mon, 2009-01-05 at 11:56 -0600, Dimitri Sivanich wrote: > > One place we've found this happens is in update_curr(), which calculates a > > delta_exec value as follows: > > delta_exec = (unsigned long)(now - curr->exec_start); > > > > Sometimes this value will be very large, as 'now' (the rq clock time) will > > be less than 'exec_start'. When this happens, __update_curr() will > > calculate a delta_exec_weighted based on this large value and add it to the > > thread's vruntime: > > curr->vruntime += delta_exec_weighted; > > So you're saying your rq->clock = sched_clock_cpu(cpu) = sched_clock() > [on ia64] goes backwards? > > If so, then that's an architecture bug, sched_clock() must never be seen > to go backwards!
Actually, sched_clock() should not go backwards on any one cpu, but the readings will be different between cpus.
Also, we noticed the following code is being used for sched_clock_cpu(): u64 sched_clock_cpu(int cpu) { if (unlikely(!sched_clock_running)) return 0; return sched_clock(); }
and is called when smp_processor_id() != cpu.
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