From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757243AbbCCQhz (ORCPT ); Tue, 3 Mar 2015 11:37:55 -0500 Received: from e34.co.us.ibm.com ([32.97.110.152]:58179 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757166AbbCCQhu (ORCPT ); Tue, 3 Mar 2015 11:37:50 -0500 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: 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, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 2/6] documentation: Update based on on-demand vmstat workers Date: Tue, 3 Mar 2015 08:37:36 -0800 Message-Id: <1425400660-6380-2-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.5 In-Reply-To: <1425400660-6380-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20150303163714.GA5427@linux.vnet.ibm.com> <1425400660-6380-1-git-send-email-paulmck@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15030316-0017-0000-0000-0000092E23D5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" Now that the on-demand vmstat workers commit is in mainline, it is possible to eliminate vmstat_update()-induced OS jitter. This commit updates the documentation accordingly. Signed-off-by: Paul E. McKenney --- Documentation/kernel-per-CPU-kthreads.txt | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/Documentation/kernel-per-CPU-kthreads.txt b/Documentation/kernel-per-CPU-kthreads.txt index f3cd299fcc41..81fe051c4447 100644 --- a/Documentation/kernel-per-CPU-kthreads.txt +++ b/Documentation/kernel-per-CPU-kthreads.txt @@ -190,14 +190,16 @@ To reduce its OS jitter, do any of the following: on each CPU, including cs_dbs_timer() and od_dbs_timer(). WARNING: Please check your CPU specifications to make sure that this is safe on your particular system. - d. It is not possible to entirely get rid of OS jitter - from vmstat_update() on CONFIG_SMP=y systems, but you - can decrease its frequency by writing a large value - to /proc/sys/vm/stat_interval. The default value is - HZ, for an interval of one second. Of course, larger - values will make your virtual-memory statistics update - more slowly. Of course, you can also run your workload - at a real-time priority, thus preempting vmstat_update(), + d. As of v3.18, Christoph Lameter's on-demand vmstat workers + commit prevents OS jitter due to vmstat_update() on + CONFIG_SMP=y systems. Before v3.18, is not possible + to entirely get rid of the OS jitter, but you can + decrease its frequency by writing a large value to + /proc/sys/vm/stat_interval. The default value is HZ, + for an interval of one second. Of course, larger values + will make your virtual-memory statistics update more + slowly. Of course, you can also run your workload at + a real-time priority, thus preempting vmstat_update(), but if your workload is CPU-bound, this is a bad idea. However, there is an RFC patch from Christoph Lameter (based on an earlier one from Gilad Ben-Yossef) that -- 1.8.1.5