On 2014/5/27 17:55, Mike Galbraith wrote: > On Tue, 2014-05-27 at 15:56 +0800, Libo Chen wrote: >> > On 2014/5/26 22:19, Mike Galbraith wrote: >>> > > On Mon, 2014-05-26 at 20:16 +0800, Libo Chen wrote: >>>> > >> On 2014/5/26 13:11, Mike Galbraith wrote: >>> > > >>>>> > >>> Your synthetic test is the absolute worst case scenario. There has >>>>> > >>> to >>>>> > >>> be work between wakeups for select_idle_sibling() to have any chance >>>>> > >>> whatsoever of turning in a win. At 0 work, it becomes 100% >>>>> > >>> overhead. >>>> > >> >>>> > >> not synthetic, it is a real problem in our product. under no load, >>>> > >> waste >>>> > >> much cpu time. >>> > > >>> > > What happens in your product if you apply the commit I pointed out? >> > >> > under no load, cpu usage is up to 60%, but the same apps cost 10% on >> > susp sp1. The apps use a lot of timer. > Something is rotten. 3.14-rt contains that commit, I ran your test with > 256 threads on 64 core box, saw ~4%. > > Putting master/nopreempt config on box and doing the same test, box is > chewing up truckloads of CPU, but not from migrations. > > perf top -g --sort=symbol in my box:
perf top -g --sort=symbol Events: 3K cycles 73.27% [k] read_hpet 4.30% [k] _raw_spin_lock_irqsave 1.88% [k] __schedule 1.00% [k] idle_cpu 0.91% [k] native_write_msr_safe 0.68% [k] select_task_rq_fair 0.51% [k] module_get_kallsym 0.49% [.] sem_post 0.44% [.] main 0.41% [k] menu_select 0.39% [k] _raw_spin_lock 0.38% [k] __switch_to 0.33% [k] _raw_spin_lock_irq 0.32% [k] format_decode 0.29% [.] usleep 0.28% [.] symbols__insert 0.27% [k] tick_nohz_stop_sched_tick 0.27% [k] update_stats_wait_end 0.26% [k] apic_timer_interrupt 0.25% [k] enqueue_entity 0.25% [k] sched_clock_local 0.24% [k] _raw_spin_unlock_irqrestore 0.24% [k] select_idle_sibling 0.22% [k] number 0.22% [k] kallsyms_expand_symbol 0.21% [k] rcu_irq_exit 0.20% [k] ktime_get 0.20% [k] rb_insert_color 0.20% [k] set_next_entity 0.19% [k] vsnprintf 0.19% [k] try_to_wake_up 0.18% [k] __hrtimer_start_range_ns 0.18% [k] update_cfs_load 0.17% [k] rcu_idle_exit_common 0.17% [k] do_nanosleep 0.17% [.] __GI___libc_nanosleep 0.17% [k] trace_hardirqs_off 0.16% [k] irq_exit 0.16% [k] timerqueue_add -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
