From: Wanpeng Li <kernellwp@gmail.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>,
"Sean Christopherson" <sean.j.christopherson@intel.com>,
"Vitaly Kuznetsov" <vkuznets@redhat.com>,
"Wanpeng Li" <wanpengli@tencent.com>,
"Jim Mattson" <jmattson@google.com>,
"Joerg Roedel" <joro@8bytes.org>,
"Peter Zijlstra" <peterz@infradead.org>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@kernel.org>,
"Waiman Long" <longman@redhat.com>,
loobinliu@tencent.com, stable@vger.kernel.org
Subject: [PATCH] Revert "locking/pvqspinlock: Don't wait if vCPU is preempted"
Date: Mon, 9 Sep 2019 09:40:28 +0800 [thread overview]
Message-ID: <1567993228-23668-1-git-send-email-wanpengli@tencent.com> (raw)
From: Wanpeng Li <wanpengli@tencent.com>
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: loobinliu@tencent.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: loobinliu@tencent.com
Cc: stable@vger.kernel.org
Fixes: 75437bb304b20 (locking/pvqspinlock: Don't wait if vCPU is preempted)
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
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
next reply other threads:[~2019-09-09 1:40 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-09 1:40 Wanpeng Li [this message]
2019-09-09 10:56 ` [PATCH] Revert "locking/pvqspinlock: Don't wait if vCPU is preempted" Waiman Long
2019-09-09 11:06 ` Paolo Bonzini
2019-09-09 12:16 ` Wanpeng Li
2019-09-10 5:56 ` Wanpeng Li
2019-09-11 4:25 ` Waiman Long
2019-09-11 13:04 ` Paolo Bonzini
2019-09-25 3:15 ` Wanpeng Li
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