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 Original line 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().

		on each CPU, including cs_dbs_timer() and od_dbs_timer().

		WARNING:  Please check your CPU specifications to

		WARNING:  Please check your CPU specifications to

		make sure that this is safe on your particular system.

		make sure that this is safe on your particular system.

	d.	It is not possible to entirely get rid of OS jitter

	d.	As of v3.18, Christoph Lameter's on-demand vmstat workers

		from vmstat_update() on CONFIG_SMP=y systems, but you

		commit prevents OS jitter due to vmstat_update() on

		can decrease its frequency by writing a large value

		CONFIG_SMP=y systems.  Before v3.18, is not possible

		to /proc/sys/vm/stat_interval.	The default value is

		to entirely get rid of the OS jitter, but you can

		HZ, for an interval of one second.  Of course, larger

		decrease its frequency by writing a large value to

		values will make your virtual-memory statistics update

		/proc/sys/vm/stat_interval.  The default value is HZ,

		more slowly.  Of course, you can also run your workload

		for an interval of one second.	Of course, larger values

		at a real-time priority, thus preempting vmstat_update(),

		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.

		but if your workload is CPU-bound, this is a bad idea.

		However, there is an RFC patch from Christoph Lameter

		However, there is an RFC patch from Christoph Lameter

		(based on an earlier one from Gilad Ben-Yossef) that

		(based on an earlier one from Gilad Ben-Yossef) that