Re: [Xen-devel] [PATCH 22/24] xen: credit2: "relax" CSCHED2_MAX_TIMER

[George Dunlap]

On 17/08/16 18:20, Dario Faggioli wrote:
> 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 

We might as well toss this one in:

Reviewed-by: George Dunlap 


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[Xen-devel] [PATCH 22/24] xen: credit2: "relax" CSCHED2_MAX_TIMER

[Dario Faggioli]

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 
---
Cc: George Dunlap 
Cc: Anshul Makkar 
---
 xen/common/sched_credit2.c |2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index 21b1f91..6963872 100644
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -152,7 +152,7 @@
 /* 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_TIMERMILLISECS(2)
+#define CSCHED2_MAX_TIMERCSCHED2_CREDIT_INIT
 
 
 #define CSCHED2_IDLE_CREDIT (-(1<<30))


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