xen: credit2: "relax" CSCHED2_MAX_TIMER

Credit2 is already event based, rather than tick
based. This means, the time at which the (i+1)-eth
scheduling decision needs to happen is computed
during the i-eth scheduling decision, and a timer
is set accordingly.

If there's nothing imminent (or, the most imminent
event is really really really far away), it is
ok to say "well, let's double-check things in
a little bit anyway", but such 'little bit' does
not need to be too little, as, most likely, it's
just pure overhead.

The current period, for this "safety catch"-alike
timer is 2ms, which indeed is high, but it can
well be higher. In fact, benchmarks show that
setting it to 10ms --combined with other
optimizations-- does actually improve performance.

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>

diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index 6b983190ca4478dea1f571ce37c3cf421f4c36e9..fe46e804871ca0d6a0fde7766dbd16686b760b05 100644 (file)
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -149,7 +149,7 @@
 /* Reset: Value below which credit will be reset. */
 #define CSCHED2_CREDIT_RESET         0
 /* Max timer: Maximum time a guest can be run for. */
-#define CSCHED2_MAX_TIMER            MILLISECS(2)
+#define CSCHED2_MAX_TIMER            CSCHED2_CREDIT_INIT
 
 
 #define CSCHED2_IDLE_CREDIT                 (-(1<<30))