Messages in this thread | | | Date | Fri, 18 Nov 2011 23:39:46 +0800 | Subject | Re: [patch 1/6] sched: use rt.nr_cpus_allowed to recover select_task_rq() cycles | From | Hillf Danton <> |
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On Fri, Nov 18, 2011 at 11:17 PM, Mike Galbraith <efault@gmx.de> wrote: > > rt.nr_cpus_allowed is always available, use it to bail from select_task_rq() > when only one cpu can be used, and saves some cycles for pinned tasks. > > taskset -c 3 pipe-test > > PerfTop: 997 irqs/sec kernel:89.5% exact: 0.0% [1000Hz cycles], (all, CPU: 3) > ------------------------------------------------------------------------------------------------ > > Virgin Patched > samples pcnt function samples pcnt function > _______ _____ ___________________________ _______ _____ ___________________________ > > 2880.00 10.2% __schedule 3136.00 11.3% __schedule > 1634.00 5.8% pipe_read 1615.00 5.8% pipe_read > 1458.00 5.2% system_call 1534.00 5.5% system_call > 1382.00 4.9% _raw_spin_lock_irqsave 1412.00 5.1% _raw_spin_lock_irqsave > 1202.00 4.3% pipe_write 1255.00 4.5% copy_user_generic_string > 1164.00 4.1% copy_user_generic_string 1241.00 4.5% __switch_to > 1097.00 3.9% __switch_to 929.00 3.3% mutex_lock > 872.00 3.1% mutex_lock 846.00 3.0% mutex_unlock > 687.00 2.4% mutex_unlock 804.00 2.9% pipe_write > 682.00 2.4% native_sched_clock 713.00 2.6% native_sched_clock > 643.00 2.3% system_call_after_swapgs 653.00 2.3% _raw_spin_unlock_irqrestore > 617.00 2.2% sched_clock_local 633.00 2.3% fsnotify > 612.00 2.2% fsnotify 605.00 2.2% sched_clock_local > 596.00 2.1% _raw_spin_unlock_irqrestore 593.00 2.1% system_call_after_swapgs > 542.00 1.9% sysret_check 559.00 2.0% sysret_check > 467.00 1.7% fget_light 472.00 1.7% fget_light > 462.00 1.6% finish_task_switch 461.00 1.7% finish_task_switch > 437.00 1.5% vfs_write 442.00 1.6% vfs_write > 431.00 1.5% do_sync_write 428.00 1.5% do_sync_write > * 413.00 1.5% select_task_rq_fair 404.00 1.5% _raw_spin_lock_irq > 386.00 1.4% update_curr 402.00 1.4% update_curr > 385.00 1.4% rw_verify_area 389.00 1.4% do_sync_read > 377.00 1.3% _raw_spin_lock_irq 378.00 1.4% vfs_read > 369.00 1.3% do_sync_read 340.00 1.2% pipe_iov_copy_from_user > 360.00 1.3% vfs_read 316.00 1.1% __wake_up_sync_key > 342.00 1.2% hrtick_start_fair 313.00 1.1% __wake_up_common > > Signed-off-by: Mike Galbraith <efault@gmx.de> >
Acked-by: Hillf Danton <dhillf@gmail.com>
> --- > kernel/sched_fair.c | 3 +++ > kernel/sched_rt.c | 3 +++ > 2 files changed, 6 insertions(+) > > Index: linux-3.2.git/kernel/sched_fair.c > =================================================================== > --- linux-3.2.git.orig/kernel/sched_fair.c > +++ linux-3.2.git/kernel/sched_fair.c > @@ -2340,6 +2340,9 @@ select_task_rq_fair(struct task_struct * > int want_sd = 1; > int sync = wake_flags & WF_SYNC; > > + if (p->rt.nr_cpus_allowed < 2) > + return prev_cpu; > + > if (sd_flag & SD_BALANCE_WAKE) { > if (cpumask_test_cpu(cpu, tsk_cpus_allowed(p))) > want_affine = 1; > Index: linux-3.2.git/kernel/sched_rt.c > =================================================================== > --- linux-3.2.git.orig/kernel/sched_rt.c > +++ linux-3.2.git/kernel/sched_rt.c > @@ -999,6 +999,9 @@ select_task_rq_rt(struct task_struct *p, > > cpu = task_cpu(p); > > + if (p->rt.nr_cpus_allowed < 2) > + goto out; > + > /* For anything but wake ups, just return the task_cpu */ > if (sd_flag != SD_BALANCE_WAKE && sd_flag != SD_BALANCE_FORK) > goto out; > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > > >
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