From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx164.postini.com [74.125.245.164]) by kanga.kvack.org (Postfix) with SMTP id AA8896B0032 for ; Thu, 8 Aug 2013 02:54:15 -0400 (EDT) Received: by mail-la0-f45.google.com with SMTP id fj20so1845603lab.32 for ; Wed, 07 Aug 2013 23:54:13 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <0000013f61e7609b-a8d1907b-8169-4f77-ab83-a624a8d0ab4a-000000@email.amazonses.com> References: <1371672168-9869-1-git-send-email-gilad@benyossef.com> <0000013f61e7609b-a8d1907b-8169-4f77-ab83-a624a8d0ab4a-000000@email.amazonses.com> Date: Thu, 8 Aug 2013 09:54:13 +0300 Message-ID: Subject: Re: [PATCH v2 1/2] mm: make vmstat_update periodic run conditional From: Gilad Ben-Yossef Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter Cc: "Paul E. McKenney" , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Frederic Weisbecker On Thu, Jun 20, 2013 at 5:05 PM, Christoph Lameter wrote: > > On Wed, 19 Jun 2013, Gilad Ben-Yossef wrote: > > > +static void vmstat_update(struct work_struct *w) > > +{ > > + int cpu, this_cpu = smp_processor_id(); > > + > > + if (unlikely(this_cpu == vmstat_monitor_cpu)) > > + for_each_cpu_not(cpu, &vmstat_cpus) > > + if (need_vmstat(cpu)) > > + start_cpu_timer(cpu); > > + > > + if (likely(refresh_cpu_vm_stats(this_cpu) || (this_cpu == > > vmstat_monitor_cpu))) > > + schedule_delayed_work(&__get_cpu_var(vmstat_work), > > + > > round_jiffies_relative(sysctl_stat_interval)); > > + else > > + cpumask_clear_cpu(this_cpu, &vmstat_cpus); > > The clearing of vmstat_cpus could be avoided if this processor is not > running tickless. Frequent updates to vmstat_cpus could become an issue. I like the idea of tying the vmstat disabling to the tickless logic but I seem to have run into a bit of a chicken and egg problem here: vmstat_update runs from the vmstat work queue item by the workqueue kernel thread. If this code is running, it means there are at least two schedulable tasks: 1. The workqueue kernel thread, because it is running. 2. At least one more task, otherwise were were in idle and the workqueue kernel thread would not execute this work item. Unfortunately, having two schedulable tasks means we're not running tickless, so the check will never trigger - or have I've missed something obvious? Thanks, Gilad -- Gilad Ben-Yossef Chief Coffee Drinker gilad@benyossef.com Israel Cell: +972-52-8260388 US Cell: +1-973-8260388 http://benyossef.com "If you take a class in large-scale robotics, can you end up in a situation where the homework eats your dog?" -- Jean-Baptiste Queru -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org