From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753360AbbKWQUP (ORCPT ); Mon, 23 Nov 2015 11:20:15 -0500 Received: from terminus.zytor.com ([198.137.202.10]:44330 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753541AbbKWQUL (ORCPT ); Mon, 23 Nov 2015 11:20:11 -0500 Date: Mon, 23 Nov 2015 08:19:30 -0800 From: tip-bot for Rik van Riel Message-ID: Cc: peterz@infradead.org, tglx@linutronix.de, linux-kernel@vger.kernel.org, hpa@zytor.com, jstancek@redhat.com, riel@redhat.com, mingo@kernel.org, torvalds@linux-foundation.org, efault@gmx.de Reply-To: riel@redhat.com, torvalds@linux-foundation.org, efault@gmx.de, mingo@kernel.org, peterz@infradead.org, tglx@linutronix.de, jstancek@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org In-Reply-To: <1446756983-28173-3-git-send-email-riel@redhat.com> References: <1446756983-28173-3-git-send-email-riel@redhat.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/core] sched/numa: Cap PTE scanning overhead to 3% of run time Git-Commit-ID: 51170840fe91dfca10fd533b303ea39b2524782a X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 51170840fe91dfca10fd533b303ea39b2524782a Gitweb: http://git.kernel.org/tip/51170840fe91dfca10fd533b303ea39b2524782a Author: Rik van Riel AuthorDate: Thu, 5 Nov 2015 15:56:23 -0500 Committer: Ingo Molnar CommitDate: Mon, 23 Nov 2015 09:37:54 +0100 sched/numa: Cap PTE scanning overhead to 3% of run time There is a fundamental mismatch between the runtime based NUMA scanning at the task level, and the wall clock time NUMA scanning at the mm level. On a severely overloaded system, with very large processes, this mismatch can cause the system to spend all of its time in change_prot_numa(). This can happen if the task spends at least two ticks in change_prot_numa(), and only gets two ticks of CPU time in the real time between two scan intervals of the mm. This patch ensures that a task never spends more than 3% of run time scanning PTEs. It does that by ensuring that in-between task_numa_work() runs, the task spends at least 32x as much time on other things than it did on task_numa_work(). This is done stochastically: if a timer tick happens, or the task gets rescheduled during task_numa_work(), we delay a future run of task_numa_work() until the task has spent at least 32x the amount of CPU time doing something else, as it spent inside task_numa_work(). The longer task_numa_work() takes, the more likely it is this happens. If task_numa_work() takes very little time, chances are low that that code will do anything, but we will not care. Reported-and-tested-by: Jan Stancek Signed-off-by: Rik van Riel Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: mgorman@suse.de Link: http://lkml.kernel.org/r/1446756983-28173-3-git-send-email-riel@redhat.com Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 309b1d5..95b944e 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2155,6 +2155,7 @@ void task_numa_work(struct callback_head *work) unsigned long migrate, next_scan, now = jiffies; struct task_struct *p = current; struct mm_struct *mm = p->mm; + u64 runtime = p->se.sum_exec_runtime; struct vm_area_struct *vma; unsigned long start, end; unsigned long nr_pte_updates = 0; @@ -2277,6 +2278,17 @@ out: else reset_ptenuma_scan(p); up_read(&mm->mmap_sem); + + /* + * Make sure tasks use at least 32x as much time to run other code + * than they used here, to limit NUMA PTE scanning overhead to 3% max. + * Usually update_task_scan_period slows down scanning enough; on an + * overloaded system we need to limit overhead on a per task basis. + */ + if (unlikely(p->se.sum_exec_runtime != runtime)) { + u64 diff = p->se.sum_exec_runtime - runtime; + p->node_stamp += 32 * diff; + } } /*