From: Wanpeng Li <[email protected]>
This patch reverts commit 75437bb304b20 (locking/pvqspinlock: Don't wait if
vCPU is preempted), we found great regression caused by this commit.
Xeon Skylake box, 2 sockets, 40 cores, 80 threads, three VMs, each is 80 vCPUs.
The score of ebizzy -M can reduce from 13000-14000 records/s to 1700-1800
records/s with this commit.
Host Guest score
vanilla + w/o kvm optimizes vanilla 1700-1800 records/s
vanilla + w/o kvm optimizes vanilla + revert 13000-14000 records/s
vanilla + w/ kvm optimizes vanilla 4500-5000 records/s
vanilla + w/ kvm optimizes vanilla + revert 14000-15500 records/s
Exit from aggressive wait-early mechanism can result in yield premature and
incur extra scheduling latency in over-subscribe scenario.
kvm optimizes:
[1] commit d73eb57b80b (KVM: Boost vCPUs that are delivering interrupts)
[2] commit 266e85a5ec9 (KVM: X86: Boost queue head vCPU to mitigate lock waiter
preemption)
Tested-by: [email protected]
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Radim Krčmář <[email protected]>
Cc: [email protected]
Cc: [email protected]
Fixes: 75437bb304b20 (locking/pvqspinlock: Don't wait if vCPU is preempted)
Signed-off-by: Wanpeng Li <[email protected]>
---
kernel/locking/qspinlock_paravirt.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/locking/qspinlock_paravirt.h
b/kernel/locking/qspinlock_paravirt.h
index 89bab07..e84d21a 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -269,7 +269,7 @@ pv_wait_early(struct pv_node *prev, int loop)
if ((loop & PV_PREV_CHECK_MASK) != 0)
return false;
- return READ_ONCE(prev->state) != vcpu_running ||
vcpu_is_preempted(prev->cpu);
+ return READ_ONCE(prev->state) != vcpu_running;
}
/*
--
2.7.4
