[Xen-devel] [PATCH 03/24] xen: credit1: return the 'time remaining to the limit' as next timeslice.

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

If vcpu x has run for 200us, and sched_ratelimit_us is
1000us, continue running x _but_ return 1000us-200us as
the next time slice. This way, next scheduling point will
happen in 800us, i.e., exactly at the point when x crosses
the threshold, and can be descheduled (if appropriate).

Right now (without this patch), we're always returning
sched_ratelimit_us (1000us, in the example above), which
means we're (potentially) allowing x to run more than
it should have been able to (even when considering rate
limiting into account).

Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
---
Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
---
 xen/common/sched_credit.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c
index 3d4f223..3f439a0 100644
--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -1782,7 +1782,7 @@ csched_schedule(
         snext = scurr;
         snext->start_time += now;
         perfc_incr(delay_ms);
-        tslice = MICROSECS(prv->ratelimit_us);
+        tslice = MICROSECS(prv->ratelimit_us) - runtime;
         ret.migrated = 0;
         goto out;
     }


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