kthread: Add pointer to vmstat-avoidance patch

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

diff --git a/Documentation/kernel-per-CPU-kthreads.txt b/Documentation/kernel-per-CPU-kthreads.txt
index 32351bf..827104f 100644 (file)
--- a/Documentation/kernel-per-CPU-kthreads.txt
+++ b/Documentation/kernel-per-CPU-kthreads.txt
@@ -181,12 +181,17 @@ To reduce its OS jitter, do any of the following:
                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().
+               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
+               reduces or even eliminates vmstat overhead for some
+               workloads at https://lkml.org/lkml/2013/9/4/379.
        e.      If running on high-end powerpc servers, build with
                CONFIG_PPC_RTAS_DAEMON=n.  This prevents the RTAS
                daemon from running on each CPU every second or so.