From 5c8c0ae7c45ef45acde29638fa342c2d721ae70a Mon Sep 17 00:00:00 2001 From: Eslam Elnikety Date: Fri, 3 May 2019 19:43:49 +0000 Subject: [PATCH] sched/credit: avoid priority boost for capped domains when unpark When unpausing a capped domain, the scheduler currently clears the CSCHED_FLAG_VCPU_PARKED flag before vcpu_wake(). This, in turn, causes the vcpu_wake to set CSCHED_PRI_TS_BOOST, resulting in an unfair credit boost. The comment around the changed lines already states that clearing the flag should happen AFTER the unpause. This bug was introduced in commit be650750945 "credit1: Use atomic bit operations for the flags structure". Original patch author credit: Xi Xiong while at Amazon. Signed-off-by: Eslam Elnikety Reviewed-by: Leonard Foerster Reviewed-by: Petre Eftime Acked-by: Dario Faggioli --- xen/common/sched_credit.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c index 3abe20def8..7b7facbace 100644 --- a/xen/common/sched_credit.c +++ b/xen/common/sched_credit.c @@ -1538,7 +1538,7 @@ csched_acct(void* dummy) svc->pri = CSCHED_PRI_TS_UNDER; /* Unpark any capped domains whose credits go positive */ - if ( test_and_clear_bit(CSCHED_FLAG_VCPU_PARKED, &svc->flags) ) + if ( test_bit(CSCHED_FLAG_VCPU_PARKED, &svc->flags) ) { /* * It's important to unset the flag AFTER the unpause() @@ -1547,6 +1547,7 @@ csched_acct(void* dummy) */ SCHED_STAT_CRANK(vcpu_unpark); vcpu_unpause(svc->vcpu); + clear_bit(CSCHED_FLAG_VCPU_PARKED, &svc->flags); } /* Upper bound on credits means VCPU stops earning */ -- 2.30.2