Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 89bf5d82 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

documentation: Update based on on-demand vmstat workers 



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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent d2af1ad7

Documentation/kernel-per-CPU-kthreads.txt

+10 −8
Original line number Diff line number Diff line
@@ -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