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: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/Documentation/kernel-per-CPU-kthreads.txt b/Documentation/kernel-per-CPU-kthreads.txt
index f3cd299fcc41203f9fe73ad16cd70aa77a421ef3..81fe051c444715c1fb7be584b29a35ba93736861 100644 (file)
--- 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