On 02/03/17 10:38, Dario Faggioli wrote:
Chacking whether or not a vCPU can be 'stolen'
from a peer pCPU's runqueue is relatively cheap.
Therefore, let's do that as early as possible,
avoiding potentially useless complex checks, and
cpumask manipulations.
Signed-off-by: Dario Faggioli <dario.faggi...@citrix.com>
---
Cc: George Dunlap <george.dun...@eu.citrix.com>
---
xen/common/sched_credit.c | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)
diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c
index 63a8675..2b13e99 100644
--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -708,12 +708,10 @@ static inline int
__csched_vcpu_is_migrateable(struct vcpu *vc, int dest_cpu, cpumask_t *mask)
{
/*
- * Don't pick up work that's in the peer's scheduling tail or hot on
- * peer PCPU. Only pick up work that prefers and/or is allowed to run
- * on our CPU.
+ * Don't pick up work that's or hot on peer PCPU, or that can't (or
Not clear.
+ * would prefer not to) run on cpu.
*/
- return !vc->is_running &&
- !__csched_vcpu_is_cache_hot(vc) &&
+ return !__csched_vcpu_is_cache_hot(vc) &&
cpumask_test_cpu(dest_cpu, mask);
!vc->is_running doesn't ease the complexity and doesn't save much on cpu
cycles. Infact, I think (!vc->is_running) makes the intention to check
for migration much more clear to understand.
Yeah, apart from the above reasons, its save to remove this check from here.
}
@@ -1622,7 +1620,9 @@ csched_runq_steal(int peer_cpu, int cpu, int pri, int balance_step)
BUG_ON( is_idle_vcpu(vc) );
/*
- * If the vcpu has no useful soft affinity, skip this vcpu.
+ * If the vcpu is still in peer_cpu's scheduling tail, or if it
+ * has no useful soft affinity, skip it.
+ *
* In fact, what we want is to check if we have any "soft-affine
* work" to steal, before starting to look at "hard-affine work".
*
@@ -1633,8 +1633,9 @@ csched_runq_steal(int peer_cpu, int cpu, int pri, int
balance_step)
* vCPUs with useful soft affinities in some sort of bitmap
* or counter.
*/
- if ( balance_step == CSCHED_BALANCE_SOFT_AFFINITY
- && !__vcpu_has_soft_affinity(vc, vc->cpu_hard_affinity) )
+ if ( vc->is_running ||
+ (balance_step == CSCHED_BALANCE_SOFT_AFFINITY
+ && !__vcpu_has_soft_affinity(vc, vc->cpu_hard_affinity)) )
continue;
csched_balance_cpumask(vc, balance_step, cpumask_scratch);
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