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From: Mike Galbraith <mgalbraith@suse.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@elte.hu>, Paul Turner <pjt@google.com>
Subject: [patch 1/7] sched: use rt.nr_cpus_allowed to recover select_task_rq() cycles
Date: Tue, 22 Nov 2011 15:18:24 +0100
Message-ID: <1321971504.6855.15.camel@marge.simson.net> (raw)
In-Reply-To: <1321971445.6855.14.camel@marge.simson.net>


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>

---
 kernel/sched/fair.c |    3 +++
 kernel/sched/rt.c   |    3 +++
 2 files changed, 6 insertions(+)

Index: linux-3.0-tip/kernel/sched/fair.c
===================================================================
--- linux-3.0-tip.orig/kernel/sched/fair.c
+++ linux-3.0-tip/kernel/sched/fair.c
@@ -2730,6 +2730,9 @@ select_task_rq_fair(struct task_struct *
 	int want_sd = 1;
 	int sync = wake_flags & WF_SYNC;
 
+	if (p->rt.nr_cpus_allowed == 1)
+		return prev_cpu;
+
 	if (sd_flag & SD_BALANCE_WAKE) {
 		if (cpumask_test_cpu(cpu, tsk_cpus_allowed(p)))
 			want_affine = 1;
Index: linux-3.0-tip/kernel/sched/rt.c
===================================================================
--- linux-3.0-tip.orig/kernel/sched/rt.c
+++ linux-3.0-tip/kernel/sched/rt.c
@@ -1200,6 +1200,9 @@ select_task_rq_rt(struct task_struct *p,
 
 	cpu = task_cpu(p);
 
+	if (p->rt.nr_cpus_allowed == 1)
+		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;




  reply index

Thread overview: 79+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-11-15  9:46 sched: Avoid SMT siblings in select_idle_sibling() if possible Peter Zijlstra
2011-11-16  1:14 ` Suresh Siddha
2011-11-16  9:24   ` Mike Galbraith
2011-11-16 18:37     ` Suresh Siddha
2011-11-17  1:59       ` Mike Galbraith
2011-11-17 15:38         ` Mike Galbraith
2011-11-17 15:56           ` Peter Zijlstra
2011-11-17 16:38             ` Mike Galbraith
2011-11-17 17:36               ` Suresh Siddha
2011-11-18 15:14                 ` Mike Galbraith
2011-11-18 15:17                   ` [patch 1/6] sched: use rt.nr_cpus_allowed to recover select_task_rq() cycles Mike Galbraith
2011-11-18 15:35                     ` Peter Zijlstra
2011-11-18 17:34                       ` Mike Galbraith
2011-11-22 14:17                       ` Mike Galbraith
2011-11-22 14:18                         ` Mike Galbraith [this message]
2011-12-06  9:50                           ` [tip:sched/core] sched: Use " tip-bot for Mike Galbraith
2011-11-22 14:20                         ` [patch 2/7] sched: save some hrtick_start_fair cycles Mike Galbraith
2011-12-06 20:20                           ` [tip:sched/core] sched: Save " tip-bot for Mike Galbraith
2011-11-22 14:21                         ` [patch 3/7] sched: set skip_clock_update in yield_task_fair() Mike Galbraith
2011-11-23 11:53                           ` Peter Zijlstra
2011-11-23 12:06                             ` Mike Galbraith
2011-11-23 14:48                           ` Peter Zijlstra
2011-11-24  3:50                             ` Mike Galbraith
2011-11-24 10:12                               ` Peter Zijlstra
2011-11-25  6:39                                 ` Mike Galbraith
2011-12-06  9:51                           ` [tip:sched/core] sched: Set " tip-bot for Mike Galbraith
2011-11-22 14:22                         ` [patch 4/7] sched: convert rq->avg_idle to rq->avg_event Mike Galbraith
2011-11-23 11:55                           ` Peter Zijlstra
2011-11-23 12:09                             ` Mike Galbraith
2011-11-23 12:27                               ` Peter Zijlstra
2011-11-23 12:57                                 ` Mike Galbraith
2011-11-23 14:21                                   ` Mike Galbraith
2011-11-22 14:23                         ` [patch 5/7] sched: ratelimit select_idle_sibling()for sync wakeups Mike Galbraith
2011-11-22 14:24                         ` [patch 6/7] sched: use rq->avg_event to resurrect nohz ratelimiting Mike Galbraith
2011-11-23 11:57                           ` Peter Zijlstra
2011-11-23 12:35                           ` Mike Galbraith
2011-11-22 14:26                         ` [patch 7/7] sched: only use TTWU_QUEUE when waker/wakee CPUs do not share top level cache Mike Galbraith
2011-11-23 12:08                           ` Peter Zijlstra
2011-11-18 15:39                     ` [patch 1/6] sched: use rt.nr_cpus_allowed to recover select_task_rq() cycles Hillf Danton
2011-11-18 15:18                   ` [patch 2/6] sched: convert rq->avg_idle to rq->avg_event Mike Galbraith
2011-11-18 15:19                   ` [patch 3/6] sched: use rq->avg_event to resurrect nohz ratelimiting Mike Galbraith
2011-11-18 15:36                     ` Peter Zijlstra
2011-11-18 17:42                       ` Mike Galbraith
2011-11-19  0:51                         ` Van De Ven, Arjan
2011-11-19  4:15                           ` Mike Galbraith
2011-11-18 15:20                   ` [patch 4/6] sched: ratelimit select_idle_sibling()for sync wakeups Mike Galbraith
2011-11-18 15:22                   ` [patch 5/6] sched: save some hrtick_start_fair cycles Mike Galbraith
2011-11-18 15:23                   ` [patch 6/6] sched: set skip_clock_update in yield_task_fair() Mike Galbraith
2012-02-20 14:41                   ` sched: Avoid SMT siblings in select_idle_sibling() if possible Peter Zijlstra
2012-02-20 15:03                     ` Srivatsa Vaddagiri
2012-02-20 18:25                       ` Mike Galbraith
2012-02-21  0:06                         ` Srivatsa Vaddagiri
2012-02-21  6:37                           ` Mike Galbraith
2012-02-21  8:09                             ` Srivatsa Vaddagiri
2012-02-20 18:14                     ` Mike Galbraith
2012-02-20 18:15                       ` Peter Zijlstra
2012-02-20 19:07                       ` Peter Zijlstra
2012-02-21  5:43                         ` Mike Galbraith
2012-02-21  8:32                           ` Srivatsa Vaddagiri
2012-02-21  9:21                             ` Mike Galbraith
2012-02-21 10:37                               ` Peter Zijlstra
2012-02-21 14:58                                 ` Srivatsa Vaddagiri
2012-02-23 10:49                       ` Srivatsa Vaddagiri
2012-02-23 11:19                         ` Ingo Molnar
2012-02-23 12:18                           ` Srivatsa Vaddagiri
2012-02-23 11:20                         ` Srivatsa Vaddagiri
2012-02-23 11:26                           ` Ingo Molnar
2012-02-23 11:32                             ` Srivatsa Vaddagiri
2012-02-23 16:17                               ` Ingo Molnar
2012-02-23 11:21                         ` Mike Galbraith
2012-02-25  6:54                           ` Srivatsa Vaddagiri
2012-02-25  8:30                             ` Mike Galbraith
2012-02-27 22:11                               ` Suresh Siddha
2012-02-28  5:05                                 ` Mike Galbraith
2011-11-17 19:08             ` Suresh Siddha
2011-11-18 15:12               ` Peter Zijlstra
2011-11-18 15:26                 ` Mike Galbraith
2011-12-06  9:49               ` [tip:sched/core] sched: Clean up domain traversal in select_idle_sibling() tip-bot for Suresh Siddha
2011-11-18 23:40 ` [tip:sched/core] sched: Avoid SMT siblings in select_idle_sibling() if possible tip-bot for Peter Zijlstra

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