[PATCH] rcu batch tuning

This patch adds new tunables for RCU queue and finished batches.  There are
two types of controls - number of completed RCU updates invoked in a batch
(blimit) and monitoring for high rate of incoming RCUs on a cpu (qhimark,
qlowmark).

By default, the per-cpu batch limit is set to a small value.  If the input
RCU rate exceeds the high watermark, we do two things - force quiescent
state on all cpus and set the batch limit of the CPU to INTMAX.  Setting
batch limit to INTMAX forces all finished RCUs to be processed in one shot.
 If we have more than INTMAX RCUs queued up, then we have bigger problems
anyway.  Once the incoming queued RCUs fall below the low watermark, the
batch limit is set to the default.

Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 75205391b335..bad5987c4727 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1284,6 +1284,19 @@ running once the system is up.
                         New name for the ramdisk parameter.
                         See Documentation/ramdisk.txt.
 
+        rcu.blimit=     [KNL,BOOT] Set maximum number of finished
+                        RCU callbacks to process in one batch.
+
+        rcu.qhimark=    [KNL,BOOT] Set threshold of queued
+                        RCU callbacks over which batch limiting is disabled.
+
+        rcu.qlowmark=   [KNL,BOOT] Set threshold of queued
+                        RCU callbacks below which batch limiting is re-enabled.
+
+        rcu.rsinterval= [KNL,BOOT,SMP] Set the number of additional
+                        RCU callbacks to queued before forcing reschedule
+                        on all cpus.
+
         rdinit=         [KNL]
                         Format: <full_path>
                         Run specified binary instead of /init from the ramdisk,