Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753200AbaG3NXt (ORCPT ); Wed, 30 Jul 2014 09:23:49 -0400 Received: from mail-we0-f175.google.com ([74.125.82.175]:64540 "EHLO mail-we0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751502AbaG3NXo (ORCPT ); Wed, 30 Jul 2014 09:23:44 -0400 Message-ID: <1406726619.5889.17.camel@marge.simpson.net> Subject: Re: [PATCH RFC tip/core/rcu 1/9] rcu: Add call_rcu_tasks() From: Mike Galbraith To: paulmck@linux.vnet.ibm.com Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com Date: Wed, 30 Jul 2014 15:23:39 +0200 In-Reply-To: <20140729180656.GY11241@linux.vnet.ibm.com> References: <20140728225556.GA19493@linux.vnet.ibm.com> <1406588180-21933-1-git-send-email-paulmck@linux.vnet.ibm.com> <20140729081416.GR20603@laptop.programming.kicks-ass.net> <20140729172304.GA16073@linux.vnet.ibm.com> <20140729173332.GM3935@laptop> <20140729180656.GY11241@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 Content-Transfer-Encoding: 8bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2014-07-29 at 11:06 -0700, Paul E. McKenney wrote: > On Tue, Jul 29, 2014 at 07:33:32PM +0200, Peter Zijlstra wrote: > > FWIW its _the_ thing that makes nohz_full uninteresting for me. The > > required overhead is insane. But yes there are people willing to pay > > that etc.. > > It would indeed be good to reduce the overhead. I could imagine all sorts > of insane approaches involving assuming that CPU write buffers flush in > bounded time, though CPU vendors seem unwilling to make guarantees in > this area. ;-) > > Or is something other than rcu_user_enter() and rcu_user_exit() causing > the pain here? Border guards stamping visas. Note native_sched_clock(). echo 0 > sched_wakeup_granularity_ns taskset -c 3 pipe-test 1 CONFIG_NO_HZ_FULL=y 604.2 KHz CONFIG_NO_HZ_FULL=y, nohz_full=3 303.5 KHz 10.45% __schedule 8.74% native_sched_clock 10.03% system_call 5.63% __schedule 4.86% _raw_spin_lock_irqsave 4.75% _raw_spin_lock 4.51% __switch_to 4.35% reschedule_interrupt 4.31% copy_user_generic_string 3.91% _raw_spin_unlock_irqrestore 3.50% pipe_read 3.35% system_call 3.02% pipe_write 2.73% context_tracking_user_exit 2.76% mutex_lock 2.30% _raw_spin_lock_irqsave 2.30% native_sched_clock 2.08% context_tracking_user_enter 2.27% copy_page_to_iter_iovec 1.94% __switch_to 2.16% mutex_unlock 1.88% copy_user_generic_string 2.15% _raw_spin_unlock_irqrestore 1.80% account_system_time 1.86% copy_page_from_iter_iovec 1.77% rcu_eqs_enter_common.isra.42 1.85% vfs_write 1.60% pipe_read 1.67% new_sync_read 1.58% pipe_write 1.61% new_sync_write 1.39% mutex_lock 1.49% vfs_read 1.37% enqueue_task_fair 1.47% fsnotify 1.25% rcu_eqs_exit_common.isra.43 1.43% __fget_light 1.14% get_vtime_delta 1.36% enqueue_task_fair 1.11% flat_send_IPI_mask 1.28% finish_task_switch 1.07% tracesys 1.26% dequeue_task_fair 1.03% dequeue_task_fair 1.25% __sb_start_write 1.01% copy_page_to_iter_iovec 1.22% _raw_spin_lock_irq 1.01% int_check_syscall_exit_work 1.20% try_to_wake_up 0.97% vfs_write 1.16% update_curr 0.94% __context_tracking_task_switch 1.05% __fsnotify_parent 0.93% mutex_unlock 1.03% pick_next_task_fair 0.88% copy_page_from_iter_iovec 1.02% sys_write 0.87% new_sync_write 1.01% sys_read 0.86% __fget_light 1.00% __wake_up_sync_key 0.85% __sb_start_write 0.93% __wake_up_common 0.85% int_ret_from_sys_call 0.92% copy_page_to_iter 0.83% syscall_trace_leave 0.90% check_preempt_wakeup 0.78% new_sync_read 0.90% __srcu_read_lock 0.78% account_user_time 0.89% put_prev_task_fair 0.76% update_curr 0.88% copy_page_from_iter 0.74% fsnotify 0.82% __sb_end_write 0.73% try_to_wake_up 0.76% __percpu_counter_add 0.71% finish_task_switch 0.74% prepare_to_wait 0.70% _raw_spin_lock_irq 0.72% touch_atime 0.69% __wake_up_sync_key 0.71% pipe_wait 0.69% __tick_nohz_task_switch pinned endless stat("/", &buf) CONFIG_NO_HZ_FULL=y CONFIG_NO_HZ_FULL=y, nohz_full=3 17.13% system_call 8.78% system_call 11.20% kmem_cache_alloc 8.52% native_sched_clock 7.14% lockref_get_not_dead 6.02% context_tracking_user_exit 7.10% kmem_cache_free 4.53% kmem_cache_alloc 6.42% path_init 4.46% _raw_spin_lock 5.69% copy_user_generic_string 4.13% copy_user_generic_string 5.25% lockref_put_or_lock 4.01% kmem_cache_free 4.14% strncpy_from_user 3.36% context_tracking_user_enter 3.99% path_lookupat 3.25% lockref_get_not_dead 3.12% complete_walk 3.25% lockref_put_or_lock 2.91% getname_flags 2.86% rcu_eqs_enter_common.isra.42 2.88% cp_new_stat 2.84% path_init 2.79% vfs_fstatat 2.56% rcu_eqs_exit_common.isra.43 2.59% user_path_at_empty 2.52% int_check_syscall_exit_work 1.93% link_path_walk 2.51% tracesys 1.81% generic_fillattr 2.08% cp_new_stat 1.75% dput 2.00% syscall_trace_leave 1.71% filename_lookup.isra.50 1.75% complete_walk 1.66% mntput 1.69% path_lookupat 1.45% vfs_getattr_nosec 1.58% strncpy_from_user 1.04% final_putname 1.56% get_vtime_delta 1.02% SYSC_newstat 1.34% int_with_check CONFIG_NO_HZ_FULL=y, nohz_full=3 - 8.53% [kernel] [k] native_sched_clock ▒ - native_sched_clock ▒ - 96.76% local_clock ▒ - get_vtime_delta ▒ - 51.95% vtime_account_user ▒ 99.96% context_tracking_user_exit ▒ syscall_trace_enter ▒ tracesys ▒ __xstat64 ▒ __libc_start_main ▒ - 48.05% __vtime_account_system ▒ 99.96% vtime_user_enter ▒ context_tracking_user_enter ▒ syscall_trace_leave ◆ int_check_syscall_exit_work ▒ __xstat64 ▒ __libc_start_main ▒ - 3.23% get_vtime_delta ▒ 52.96% vtime_account_user ▒ context_tracking_user_exit ▒ syscall_trace_enter ▒ tracesys ▒ __xstat64 ▒ __libc_start_main ▒ 47.04% __vtime_account_system ▒ vtime_user_enter ▒ context_tracking_user_enter ▒ syscall_trace_leave ▒ int_check_syscall_exit_work ▒ __xstat64 ▒ __libc_start_main -- 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/