On Wed, 13 Nov 2013 10:21:53 -0500 Steven Rostedt <[email protected]> wrote: trace-cmd record -p function -l '*nohz*' -l account_process_tick -e sched_switch > > rcu_sche-9 0d... 6858.618033: sched_switch: rcu_sched:9 [120] > S ==> swapper/0:0 [120] > <idle>-0 0.... 6858.618082: function: > tick_nohz_idle_enter <-- cpu_startup_entry > <idle>-0 0d... 6858.618101: function: > __tick_nohz_idle_enter <-- tick_nohz_idle_enter > <idle>-0 0d.s. 6858.621499: function: > tick_nohz_stop_idle <-- tick_check_idle > <idle>-0 0d.h. 6858.621550: function: > account_process_tick <-- update_process_times > <idle>-0 0d... 6858.621769: function: tick_nohz_irq_exit > <-- irq_exit > <idle>-0 0d... 6858.621787: function: > __tick_nohz_idle_enter <-- irq_exit > <idle>-0 0d.s. 6858.625500: function: > tick_nohz_stop_idle <-- tick_check_idle > <idle>-0 0d.h. 6858.625574: function: > account_process_tick <-- update_process_times > <idle>-0 0d... 6858.625818: function: tick_nohz_irq_exit > <-- irq_exit > <idle>-0 0d... 6858.625847: function: > __tick_nohz_idle_enter <-- irq_exit > <idle>-0 0d.s. 6858.629295: function: > tick_nohz_stop_idle <-- tick_check_idle > <idle>-0 0d... 6858.629351: function: tick_nohz_irq_exit > <-- irq_exit > <idle>-0 0d... 6858.629373: function: > __tick_nohz_idle_enter <-- irq_exit > <idle>-0 0d.s. 6858.629503: function: > tick_nohz_stop_idle <-- tick_check_idle > <idle>-0 0d.h. 6858.629569: function: > account_process_tick <-- update_process_times > <idle>-0 0d... 6858.629851: function: tick_nohz_irq_exit > <-- irq_exit > <idle>-0 0d... 6858.629881: function: > __tick_nohz_idle_enter <-- irq_exit > <idle>-0 0d.s. 6858.630412: function: > tick_nohz_stop_idle <-- tick_check_idle > <idle>-0 0.N.. 6858.630550: function: > tick_nohz_idle_exit <-- cpu_startup_entry > <idle>-0 0d... 6858.630605: sched_switch: swapper/0:0 [120] > R ==> rcu_sched:9 [120] > > I'm not saying that we are actually getting into nohz, but something > with the nohz code is messing with cpu accounting.
The trace does indeed show that a tick is happening, as the config has HZ=250 (4ms) and we see a tick happen every 4ms. But for some reason, we don't update the the idle time correctly when nohz is enabled. When I say nohz is enabled, I mean that we don't have nohz=off in the command line. There seems to be some difference between having nohz=off and having nohz disabled at runtime. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
