linux-kernel - [tip:locking/core] x86/kvm: Support the vCPU preemption check

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Date:   Tue, 22 Nov 2016 04:34:42 -0800
From:   tip-bot for Pan Xinhui <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     hpa@...or.com, tglx@...utronix.de, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        xinhui.pan@...ux.vnet.ibm.com, pbonzini@...hat.com,
        peterz@...radead.org
Subject: [tip:locking/core] x86/kvm: Support the vCPU preemption check

Commit-ID:  1885aa7041c9e801e5d5b093b9dad38937ca37f6
Gitweb:     http://git.kernel.org/tip/1885aa7041c9e801e5d5b093b9dad38937ca37f6
Author:     Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
AuthorDate: Wed, 2 Nov 2016 05:08:36 -0400
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 22 Nov 2016 12:48:08 +0100

x86/kvm: Support the vCPU preemption check

Support the vcpu_is_preempted() functionality under KVM. This will
enhance lock performance on overcommitted hosts (more runnable vCPUs
than physical CPUs in the system) as doing busy waits for preempted
vCPUs will hurt system performance far worse than early yielding.

struct kvm_steal_time::preempted indicates that if one vCPU is running or
not after commit "x86, kvm/x86.c: support vCPU preempted check".

 unix benchmark result:
 host:  kernel 4.8.1, i5-4570, 4 cpus
 guest: kernel 4.8.1, 8 vcpus

         test-case                       after-patch       before-patch
 Execl Throughput                       |    18307.9 lps  |    11701.6 lps
 File Copy 1024 bufsize 2000 maxblocks  |  1352407.3 KBps |   790418.9 KBps
 File Copy 256 bufsize 500 maxblocks    |   367555.6 KBps |   222867.7 KBps
 File Copy 4096 bufsize 8000 maxblocks  |  3675649.7 KBps |  1780614.4 KBps
 Pipe Throughput                        | 11872208.7 lps  | 11855628.9 lps
 Pipe-based Context Switching           |  1495126.5 lps  |  1490533.9 lps
 Process Creation                       |    29881.2 lps  |    28572.8 lps
 Shell Scripts (1 concurrent)           |    23224.3 lpm  |    22607.4 lpm
 Shell Scripts (8 concurrent)           |     3531.4 lpm  |     3211.9 lpm
 System Call Overhead                   | 10385653.0 lps  | 10419979.0 lps

Signed-off-by: Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Paolo Bonzini <pbonzini@...hat.com>
Cc: David.Laight@...LAB.COM
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: benh@...nel.crashing.org
Cc: boqun.feng@...il.com
Cc: borntraeger@...ibm.com
Cc: bsingharora@...il.com
Cc: dave@...olabs.net
Cc: jgross@...e.com
Cc: kernellwp@...il.com
Cc: konrad.wilk@...cle.com
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: mpe@...erman.id.au
Cc: paulmck@...ux.vnet.ibm.com
Cc: paulus@...ba.org
Cc: rkrcmar@...hat.com
Cc: virtualization@...ts.linux-foundation.org
Cc: will.deacon@....com
Cc: xen-devel-request@...ts.xenproject.org
Cc: xen-devel@...ts.xenproject.org
Link: http://lkml.kernel.org/r/1478077718-37424-10-git-send-email-xinhui.pan@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/kvm.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index edbbfc8..0b48dd2 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -415,6 +415,15 @@ void kvm_disable_steal_time(void)
 	wrmsr(MSR_KVM_STEAL_TIME, 0, 0);
 }
 
+static bool kvm_vcpu_is_preempted(int cpu)
+{
+	struct kvm_steal_time *src;
+
+	src = &per_cpu(steal_time, cpu);
+
+	return !!src->preempted;
+}
+
 #ifdef CONFIG_SMP
 static void __init kvm_smp_prepare_boot_cpu(void)
 {
@@ -471,6 +480,9 @@ void __init kvm_guest_init(void)
 	if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
 		has_steal_clock = 1;
 		pv_time_ops.steal_clock = kvm_steal_clock;
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+		pv_lock_ops.vcpu_is_preempted = kvm_vcpu_is_preempted;
+#endif
 	}
 
 	if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))