linux-kernel - [PATCH tip/core/rcu 2/6] documentation: Update based on on-demand vmstat workers

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Date:	Tue,  3 Mar 2015 08:37:36 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
	bobby.prani@...il.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 2/6] documentation: Update based on on-demand vmstat workers

From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>

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 <paulmck@...ux.vnet.ibm.com>
---
 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

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