run: Affine writeback to cpu 0

Improve isolation by moving writeback workqueue to CPU 0.
Thanks to Kevin Hilman for the trick.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
diff --git a/run b/run
index 1f9a88b..ac866be 100755
--- a/run
+++ b/run
@@ -34,6 +34,9 @@
 # Shutdown nmi watchdog as it uses perf events
 sysctl -w kernel.watchdog=0
 
+# Pin the writeback workqueue to CPU0
+echo 1 > /sys/bus/workqueue/devices/writeback/cpumask
+
 DIR=/sys/kernel/debug/tracing
 echo > $DIR/trace
 echo 0 > $DIR/tracing_on