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>

1 files changed, 11 insertions, 6 deletions

diff --git a/Documentation/kernel-per-CPU-kthreads.txt b/Documentation/kernel-per-CPU-kthreads.txt
index 32351bfabf20..827104fb9364 100644
--- 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.