Messages in this thread Patch in this message | | | Date | Wed, 20 Mar 2013 16:23:34 -0700 | From | Kevin Hilman <> | Subject | Re: [PATCH 30/33] sched: Debug nohz rq clock |
| |
Hi Frederic,
On 01/07/2013 06:08 PM, Frederic Weisbecker wrote: > The runqueue clock is supposed to be periodically updated by the > tick. On full dynticks CPU we call update_nohz_rq_clock() before > reading it. Now the scheduler code is complicated enough that we > may miss some update_nohz_rq_clock() calls before reading the > runqueue clock. > > This therefore introduce a new debugging feature that detects > when the rq clock is stale due to missing updates on full > dynticks CPUs. > > This can be later expanded to debug stale clocks on dynticks-idle > CPUs.
[...]
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index e1bac76..0fef0b3 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -502,16 +502,39 @@ DECLARE_PER_CPU(struct rq, runqueues); > #define cpu_curr(cpu) (cpu_rq(cpu)->curr) > #define raw_rq() (&__raw_get_cpu_var(runqueues)) > > +static inline void rq_clock_check(struct rq *rq) > +{ > +#if defined(CONFIG_SCHED_DEBUG) && defined(CONFIG_NO_HZ_FULL) > + unsigned long long clock; > + unsigned long flags; > + int cpu; > + > + cpu = cpu_of(rq); > + if (!tick_nohz_full_cpu(cpu) || rq->curr == rq->idle) > + return; > + > + local_irq_save(flags); > + clock = sched_clock_cpu(cpu_of(rq)); > + local_irq_restore(flags); > + > + if (abs(clock - rq->clock) > (TICK_NSEC * 3)) > + WARN_ON_ONCE(1); > +#endif > +}
In working on the ARM port for full nohz, I'm hitting this warning early in the kernel boot, well before userspace starts (dump below[2].)
I've seen a few different variations of this, but the common thing for all of them is the use of wait_for_completion().
During boot, only swapper is running so it seems any waiting of sufficient length during boot will always trigger this warning. The hack below[1] avoids checking for the init task, but I'm not sure if it's the right fix.
Kevin
[1] diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index f96329b..56e74df 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -512,7 +512,8 @@ static inline void rq_clock_check(struct rq *rq) int cpu;
cpu = cpu_of(rq); - if (!tick_nohz_full_cpu(cpu) || rq->curr == rq->idle) + if (!tick_nohz_full_cpu(cpu) || rq->curr == rq->idle || + is_global_init(current)) return;
[2] Example warning dump [ 1.101013] ------------[ cut here ]------------ [ 1.105865] WARNING: at /work/kernel/linaro/dev/kernel/sched/sched.h:534 __schedule+0x510/0x790() [ 1.115051] Modules linked in: [ 1.118316] [<c00159d0>] (unwind_backtrace+0x0/0x104) from [<c054dc98>] (dump_stack+0x20/0x24) [ 1.127227] [<c054dc98>] (dump_stack+0x20/0x24) from [<c0037f58>] (warn_slowpath_common+0x5c/0x78) [ 1.136535] [<c0037f58>] (warn_slowpath_common+0x5c/0x78) from [<c0037fa0>] (warn_slowpath_null+0x2c/0x34) [ 1.146545] [<c0037fa0>] (warn_slowpath_null+0x2c/0x34) from [<c0560834>] (__schedule+0x510/0x790) [ 1.155822] [<c0560834>] (__schedule+0x510/0x790) from [<c0560ba8>] (schedule+0x40/0x80) [ 1.164215] [<c0560ba8>] (schedule+0x40/0x80) from [<c055e288>] (schedule_timeout+0x180/0x250) [ 1.173156] [<c055e288>] (schedule_timeout+0x180/0x250) from [<c05601a4>] (wait_for_common+0xb8/0x15c) [ 1.182800] [<c05601a4>] (wait_for_common+0xb8/0x15c) from [<c0560268>] (wait_for_completion+0x20/0x24) [ 1.192535] [<c0560268>] (wait_for_completion+0x20/0x24) from [<c005ce4c>] (kthread_create_on_node+0x84/0xe8) [ 1.202819] [<c005ce4c>] (kthread_create_on_node+0x84/0xe8) from [<c005732c>] (__alloc_workqueue_key+0x36c/0x440) [ 1.213470] [<c005732c>] (__alloc_workqueue_key+0x36c/0x440) from [<c052d380>] (rpc_init_mempool+0x44/0x118) [ 1.223663] [<c052d380>] (rpc_init_mempool+0x44/0x118) from [<c07f1714>] (init_sunrpc+0x10/0x6c) [ 1.232757] [<c07f1714>] (init_sunrpc+0x10/0x6c) from [<c00087f0>] (do_one_initcall+0x48/0x190) [ 1.241790] [<c00087f0>] (do_one_initcall+0x48/0x190) from [<c07c3988>] (do_basic_setup+0x9c/0xd0) [ 1.251068] [<c07c3988>] (do_basic_setup+0x9c/0xd0) from [<c07c3a88>] (kernel_init_freeable+0xcc/0x16c) [ 1.260833] [<c07c3a88>] (kernel_init_freeable+0xcc/0x16c) from [<c0548840>] (kernel_init+0x1c/0xf4) [ 1.270294] [<c0548840>] (kernel_init+0x1c/0xf4) from [<c000e390>] (ret_from_fork+0x14/0x20) [ > + > static inline u64 rq_clock(struct rq *rq) > { > + rq_clock_check(rq); > return rq->clock; > } > static inline u64 rq_clock_task(struct rq *rq) > { > + rq_clock_check(rq); > return rq->clock_task; > } > > + > #ifdef CONFIG_SMP > > #define rcu_dereference_check_sched_domain(p) \ >
| |