* [PATCH 0/3] KVM: optimize the kvm_vcpu_on_spin
@ 2017-08-07 8:44 Longpeng(Mike)
2017-08-07 8:44 ` [PATCH 1/3] KVM: add spinlock-exiting optimize framework Longpeng(Mike)
` (2 more replies)
0 siblings, 3 replies; 11+ messages in thread
From: Longpeng(Mike) @ 2017-08-07 8:44 UTC (permalink / raw)
To: pbonzini, rkrcmar
Cc: agraf, borntraeger, cohuck, christoffer.dall, marc.zyngier,
james.hogan, kvm, linux-kernel, weidong.huang, arei.gonglei,
wangxinxin.wang, longpeng.mike, david, Longpeng(Mike)
This is a simple optimization for kvm_vcpu_on_spin, the
main idea is described in patch-1's commit msg.
I did some tests base on the RFC version, the result shows
that it can improves the performance slightly.
== Geekbench-3.4.1 ==
VM1: 8U,4G, vcpu(0...7) is 1:1 pinned to pcpu(6...11,18,19)
running Geekbench-3.4.1 *10 truns*
VM2/VM3/VM4: configure is the same as VM1
stress each vcpu usage(seed by top in guest) to 40%
The comparison of each testcase's score:
(higher is better)
before after improve
Inter
single 1176.7 1179.0 0.2%
multi 3459.5 3426.5 -0.9%
Float
single 1150.5 1150.9 0.0%
multi 3364.5 3391.9 0.8%
Memory(stream)
single 1768.7 1773.1 0.2%
multi 2511.6 2557.2 1.8%
Overall
single 1284.2 1286.2 0.2%
multi 3231.4 3238.4 0.2%
== kernbench-0.42 ==
VM1: 8U,12G, vcpu(0...7) is 1:1 pinned to pcpu(6...11,18,19)
running "kernbench -n 10"
VM2/VM3/VM4: configure is the same as VM1
stress each vcpu usage(seed by top in guest) to 40%
The comparison of 'Elapsed Time':
(sooner is better)
before after improve
load -j4 12.762 12.751 0.1%
load -j32 9.743 8.955 8.1%
load -j 9.688 9.229 4.7%
Physical Machine:
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 24
On-line CPU(s) list: 0-23
Thread(s) per core: 2
Core(s) per socket: 6
Socket(s): 2
NUMA node(s): 2
Vendor ID: GenuineIntel
CPU family: 6
Model: 45
Model name: Intel(R) Xeon(R) CPU E5-2640 0 @ 2.50GHz
Stepping: 7
CPU MHz: 2799.902
BogoMIPS: 5004.67
Virtualization: VT-x
L1d cache: 32K
L1i cache: 32K
L2 cache: 256K
L3 cache: 15360K
NUMA node0 CPU(s): 0-5,12-17
NUMA node1 CPU(s): 6-11,18-23
---
Changes since RFC:
- only cache result for X86. [David & Cornlia & Paolo]
- add performance numbers. [David]
- impls arm/s390. [Christoffer & David]
- refactor the impls. [me]
---
Longpeng(Mike) (3):
KVM: add spinlock-exiting optimize framework
KVM: X86: implement the logic for spinlock optimization
KVM: implement spinlock optimization logic for arm/s390
arch/mips/kvm/mips.c | 10 ++++++++++
arch/powerpc/kvm/powerpc.c | 10 ++++++++++
arch/s390/kvm/kvm-s390.c | 10 ++++++++++
arch/x86/include/asm/kvm_host.h | 5 +++++
arch/x86/kvm/svm.c | 6 ++++++
arch/x86/kvm/vmx.c | 20 ++++++++++++++++++++
arch/x86/kvm/x86.c | 15 +++++++++++++++
include/linux/kvm_host.h | 2 ++
virt/kvm/arm/arm.c | 10 ++++++++++
virt/kvm/kvm_main.c | 4 ++++
10 files changed, 92 insertions(+)
--
1.8.3.1
^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCH 1/3] KVM: add spinlock-exiting optimize framework
2017-08-07 8:44 [PATCH 0/3] KVM: optimize the kvm_vcpu_on_spin Longpeng(Mike)
@ 2017-08-07 8:44 ` Longpeng(Mike)
2017-08-07 8:55 ` David Hildenbrand
2017-08-07 8:44 ` [PATCH 2/3] KVM: X86: implement the logic for spinlock optimization Longpeng(Mike)
2017-08-07 8:44 ` [PATCH 3/3] KVM: implement spinlock optimization logic for arm/s390 Longpeng(Mike)
2 siblings, 1 reply; 11+ messages in thread
From: Longpeng(Mike) @ 2017-08-07 8:44 UTC (permalink / raw)
To: pbonzini, rkrcmar
Cc: agraf, borntraeger, cohuck, christoffer.dall, marc.zyngier,
james.hogan, kvm, linux-kernel, weidong.huang, arei.gonglei,
wangxinxin.wang, longpeng.mike, david, Longpeng(Mike)
If the vcpu(me) exit due to request a usermode spinlock, then
the spinlock-holder may be preempted in usermode or kernmode.
But if the vcpu(me) is in kernmode, then the holder must be
preempted in kernmode, so we should choose a vcpu in kernmode
as the most eligible candidate.
For some architecture(e.g. arm/s390), spin/preempt_in_kernel()
are the same, but they are different for X86.
Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
---
arch/mips/kvm/mips.c | 10 ++++++++++
arch/powerpc/kvm/powerpc.c | 10 ++++++++++
arch/s390/kvm/kvm-s390.c | 10 ++++++++++
arch/x86/kvm/x86.c | 10 ++++++++++
include/linux/kvm_host.h | 2 ++
virt/kvm/arm/arm.c | 10 ++++++++++
virt/kvm/kvm_main.c | 4 ++++
7 files changed, 56 insertions(+)
diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index d4b2ad1..e04e6b3 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -98,6 +98,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
return !!(vcpu->arch.pending_exceptions);
}
+bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
+bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
{
return 1;
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 1a75c0b..c573ddd 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -58,6 +58,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
return !!(v->arch.pending_exceptions) || kvm_request_pending(v);
}
+bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
+bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
{
return 1;
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index af09d34..f78cdc2 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -2447,6 +2447,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
return kvm_s390_vcpu_has_irq(vcpu, 0);
}
+bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
+bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
void kvm_s390_vcpu_block(struct kvm_vcpu *vcpu)
{
atomic_or(PROG_BLOCK_SIE, &vcpu->arch.sie_block->prog20);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6c97c82..04c6a1f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8435,6 +8435,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
return kvm_vcpu_running(vcpu) || kvm_vcpu_has_events(vcpu);
}
+bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
+bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
{
return kvm_vcpu_exiting_guest_mode(vcpu) == IN_GUEST_MODE;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 890b706..9613620 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -798,6 +798,8 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
void kvm_arch_hardware_unsetup(void);
void kvm_arch_check_processor_compat(void *rtn);
int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu);
+bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu);
+bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu);
int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu);
#ifndef __KVM_HAVE_ARCH_VM_ALLOC
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index a39a1e1..e45f780 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -416,6 +416,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
&& !v->arch.power_off && !v->arch.pause);
}
+bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
+bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
/* Just ensure a guest exit from a particular CPU */
static void exit_vm_noop(void *info)
{
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f3f7427..0d0527b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2324,12 +2324,14 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
{
struct kvm *kvm = me->kvm;
struct kvm_vcpu *vcpu;
+ bool in_kern;
int last_boosted_vcpu = me->kvm->last_boosted_vcpu;
int yielded = 0;
int try = 3;
int pass;
int i;
+ in_kern = kvm_arch_vcpu_spin_in_kernel(me);
kvm_vcpu_set_in_spin_loop(me, true);
/*
* We boost the priority of a VCPU that is runnable but not
@@ -2351,6 +2353,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
continue;
if (swait_active(&vcpu->wq) && !kvm_arch_vcpu_runnable(vcpu))
continue;
+ if (in_kern && !kvm_arch_vcpu_preempt_in_kernel(vcpu))
+ continue;
if (!kvm_vcpu_eligible_for_directed_yield(vcpu))
continue;
--
1.8.3.1
^ permalink raw reply related [flat|nested] 11+ messages in thread
* [PATCH 2/3] KVM: X86: implement the logic for spinlock optimization
2017-08-07 8:44 [PATCH 0/3] KVM: optimize the kvm_vcpu_on_spin Longpeng(Mike)
2017-08-07 8:44 ` [PATCH 1/3] KVM: add spinlock-exiting optimize framework Longpeng(Mike)
@ 2017-08-07 8:44 ` Longpeng(Mike)
2017-08-07 10:45 ` Paolo Bonzini
2017-08-07 8:44 ` [PATCH 3/3] KVM: implement spinlock optimization logic for arm/s390 Longpeng(Mike)
2 siblings, 1 reply; 11+ messages in thread
From: Longpeng(Mike) @ 2017-08-07 8:44 UTC (permalink / raw)
To: pbonzini, rkrcmar
Cc: agraf, borntraeger, cohuck, christoffer.dall, marc.zyngier,
james.hogan, kvm, linux-kernel, weidong.huang, arei.gonglei,
wangxinxin.wang, longpeng.mike, david, Longpeng(Mike)
Implements the kvm_arch_vcpu_spin/preempt_in_kernel(), because get_cpl
requires vcpu_load, so we must cache the result(whether the vcpu was
preempted when its cpl=0) in kvm_arch_vcpu.
Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
---
arch/x86/include/asm/kvm_host.h | 5 +++++
arch/x86/kvm/svm.c | 6 ++++++
arch/x86/kvm/vmx.c | 20 ++++++++++++++++++++
arch/x86/kvm/x86.c | 9 +++++++--
4 files changed, 38 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 87ac4fb..d2b2d57 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -688,6 +688,9 @@ struct kvm_vcpu_arch {
/* GPA available (AMD only) */
bool gpa_available;
+
+ /* be preempted when it's in kernel-mode(cpl=0) */
+ bool preempted_in_kernel;
};
struct kvm_lpage_info {
@@ -1057,6 +1060,8 @@ struct kvm_x86_ops {
void (*cancel_hv_timer)(struct kvm_vcpu *vcpu);
void (*setup_mce)(struct kvm_vcpu *vcpu);
+
+ bool (*spin_in_kernel)(struct kvm_vcpu *vcpu);
};
struct kvm_arch_async_pf {
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 4d8141e..552ab4c 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5352,6 +5352,11 @@ static void svm_setup_mce(struct kvm_vcpu *vcpu)
vcpu->arch.mcg_cap &= 0x1ff;
}
+static bool svm_spin_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return svm_get_cpl(vcpu) == 0;
+}
+
static struct kvm_x86_ops svm_x86_ops __ro_after_init = {
.cpu_has_kvm_support = has_svm,
.disabled_by_bios = is_disabled,
@@ -5464,6 +5469,7 @@ static void svm_setup_mce(struct kvm_vcpu *vcpu)
.deliver_posted_interrupt = svm_deliver_avic_intr,
.update_pi_irte = svm_update_pi_irte,
.setup_mce = svm_setup_mce,
+ .spin_in_kernel = svm_spin_in_kernel,
};
static int __init svm_init(void)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 39a6222..d0dfe2e 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -11547,6 +11547,25 @@ static void vmx_setup_mce(struct kvm_vcpu *vcpu)
~FEATURE_CONTROL_LMCE;
}
+static bool vmx_spin_in_kernel(struct kvm_vcpu *vcpu)
+{
+ u32 secondary_exec_ctrl = 0;
+
+ /*
+ * Intel sdm vol3 ch-25.1.3 says: The “PAUSE-loop exiting”
+ * VM-execution control is ignored if CPL > 0. So the vcpu
+ * is always exiting with CPL=0 if it uses PLE.
+ *
+ * The following block needs less cycles than vmx_get_cpl().
+ */
+ if (cpu_has_secondary_exec_ctrls())
+ secondary_exec_ctrl = vmcs_read32(SECONDARY_VM_EXEC_CONTROL);
+ if (secondary_exec_ctrl & SECONDARY_EXEC_PAUSE_LOOP_EXITING)
+ return true;
+
+ return vmx_get_cpl(vcpu) == 0;
+}
+
static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
.cpu_has_kvm_support = cpu_has_kvm_support,
.disabled_by_bios = vmx_disabled_by_bios,
@@ -11674,6 +11693,7 @@ static void vmx_setup_mce(struct kvm_vcpu *vcpu)
#endif
.setup_mce = vmx_setup_mce,
+ .spin_in_kernel = vmx_spin_in_kernel,
};
static int __init vmx_init(void)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 04c6a1f..fa79a60 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2881,6 +2881,10 @@ static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
{
int idx;
+
+ if (vcpu->preempted)
+ vcpu->arch.preempted_in_kernel = !kvm_x86_ops->get_cpl(vcpu);
+
/*
* Disable page faults because we're in atomic context here.
* kvm_write_guest_offset_cached() would call might_fault()
@@ -7988,6 +7992,7 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
kvm_pmu_init(vcpu);
vcpu->arch.pending_external_vector = -1;
+ vcpu->arch.preempted_in_kernel = false;
kvm_hv_vcpu_init(vcpu);
@@ -8437,12 +8442,12 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
{
- return false;
+ return kvm_x86_ops->spin_in_kernel(vcpu);
}
bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
{
- return false;
+ return vcpu->arch.preempted_in_kernel;
}
int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
--
1.8.3.1
^ permalink raw reply related [flat|nested] 11+ messages in thread
* [PATCH 3/3] KVM: implement spinlock optimization logic for arm/s390
2017-08-07 8:44 [PATCH 0/3] KVM: optimize the kvm_vcpu_on_spin Longpeng(Mike)
2017-08-07 8:44 ` [PATCH 1/3] KVM: add spinlock-exiting optimize framework Longpeng(Mike)
2017-08-07 8:44 ` [PATCH 2/3] KVM: X86: implement the logic for spinlock optimization Longpeng(Mike)
@ 2017-08-07 8:44 ` Longpeng(Mike)
2017-08-07 8:52 ` David Hildenbrand
2 siblings, 1 reply; 11+ messages in thread
From: Longpeng(Mike) @ 2017-08-07 8:44 UTC (permalink / raw)
To: pbonzini, rkrcmar
Cc: agraf, borntraeger, cohuck, christoffer.dall, marc.zyngier,
james.hogan, kvm, linux-kernel, weidong.huang, arei.gonglei,
wangxinxin.wang, longpeng.mike, david, Longpeng(Mike)
Implements the kvm_arch_vcpu_spin/preempt_in_kernel() for arm/s390,
they needn't cache the result.
Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
---
arch/s390/kvm/kvm-s390.c | 4 ++--
virt/kvm/arm/arm.c | 4 ++--
2 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index f78cdc2..49b9178 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -2449,12 +2449,12 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
{
- return false;
+ return !(vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE);
}
bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
{
- return false;
+ return !(vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE);
}
void kvm_s390_vcpu_block(struct kvm_vcpu *vcpu)
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index e45f780..956f025 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -418,12 +418,12 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
{
- return false;
+ return vcpu_mode_priv(vcpu);
}
bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
{
- return false;
+ return vcpu_mode_priv(vcpu);
}
/* Just ensure a guest exit from a particular CPU */
--
1.8.3.1
^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [PATCH 3/3] KVM: implement spinlock optimization logic for arm/s390
2017-08-07 8:44 ` [PATCH 3/3] KVM: implement spinlock optimization logic for arm/s390 Longpeng(Mike)
@ 2017-08-07 8:52 ` David Hildenbrand
2017-08-07 8:54 ` Longpeng (Mike)
0 siblings, 1 reply; 11+ messages in thread
From: David Hildenbrand @ 2017-08-07 8:52 UTC (permalink / raw)
To: Longpeng(Mike), pbonzini, rkrcmar
Cc: agraf, borntraeger, cohuck, christoffer.dall, marc.zyngier,
james.hogan, kvm, linux-kernel, weidong.huang, arei.gonglei,
wangxinxin.wang, longpeng.mike
On 07.08.2017 10:44, Longpeng(Mike) wrote:
> Implements the kvm_arch_vcpu_spin/preempt_in_kernel() for arm/s390,
> they needn't cache the result.
>
> Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
> ---
> arch/s390/kvm/kvm-s390.c | 4 ++--
> virt/kvm/arm/arm.c | 4 ++--
> 2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index f78cdc2..49b9178 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -2449,12 +2449,12 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
>
> bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
> {
> - return false;
> + return !(vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE);
> }
>
> bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
> {
> - return false;
> + return !(vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE);
> }
>
> void kvm_s390_vcpu_block(struct kvm_vcpu *vcpu)
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index e45f780..956f025 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -418,12 +418,12 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
>
> bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
> {
> - return false;
> + return vcpu_mode_priv(vcpu);
> }
>
> bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
> {
> - return false;
> + return vcpu_mode_priv(vcpu);
> }
>
> /* Just ensure a guest exit from a particular CPU */
>
Can you split that into two parts? (arm and s390x?)
--
Thanks,
David
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 3/3] KVM: implement spinlock optimization logic for arm/s390
2017-08-07 8:52 ` David Hildenbrand
@ 2017-08-07 8:54 ` Longpeng (Mike)
0 siblings, 0 replies; 11+ messages in thread
From: Longpeng (Mike) @ 2017-08-07 8:54 UTC (permalink / raw)
To: David Hildenbrand
Cc: pbonzini, rkrcmar, agraf, borntraeger, cohuck, christoffer.dall,
marc.zyngier, james.hogan, kvm, linux-kernel, weidong.huang,
arei.gonglei, wangxinxin.wang, longpeng.mike
On 2017/8/7 16:52, David Hildenbrand wrote:
> On 07.08.2017 10:44, Longpeng(Mike) wrote:
>> Implements the kvm_arch_vcpu_spin/preempt_in_kernel() for arm/s390,
>> they needn't cache the result.
>>
>> Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
>> ---
>> arch/s390/kvm/kvm-s390.c | 4 ++--
>> virt/kvm/arm/arm.c | 4 ++--
>> 2 files changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index f78cdc2..49b9178 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -2449,12 +2449,12 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
>>
>> bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
>> {
>> - return false;
>> + return !(vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE);
>> }
>>
>> bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
>> {
>> - return false;
>> + return !(vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE);
>> }
>>
>> void kvm_s390_vcpu_block(struct kvm_vcpu *vcpu)
>> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
>> index e45f780..956f025 100644
>> --- a/virt/kvm/arm/arm.c
>> +++ b/virt/kvm/arm/arm.c
>> @@ -418,12 +418,12 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
>>
>> bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
>> {
>> - return false;
>> + return vcpu_mode_priv(vcpu);
>> }
>>
>> bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
>> {
>> - return false;
>> + return vcpu_mode_priv(vcpu);
>> }
>>
>> /* Just ensure a guest exit from a particular CPU */
>>
>
> Can you split that into two parts? (arm and s390x?)
OK, I'll split in V2. :)
>
--
Regards,
Longpeng(Mike)
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 1/3] KVM: add spinlock-exiting optimize framework
2017-08-07 8:44 ` [PATCH 1/3] KVM: add spinlock-exiting optimize framework Longpeng(Mike)
@ 2017-08-07 8:55 ` David Hildenbrand
2017-08-07 9:04 ` Longpeng (Mike)
0 siblings, 1 reply; 11+ messages in thread
From: David Hildenbrand @ 2017-08-07 8:55 UTC (permalink / raw)
To: Longpeng(Mike), pbonzini, rkrcmar
Cc: agraf, borntraeger, cohuck, christoffer.dall, marc.zyngier,
james.hogan, kvm, linux-kernel, weidong.huang, arei.gonglei,
wangxinxin.wang, longpeng.mike
On 07.08.2017 10:44, Longpeng(Mike) wrote:
> If the vcpu(me) exit due to request a usermode spinlock, then
> the spinlock-holder may be preempted in usermode or kernmode.
>
> But if the vcpu(me) is in kernmode, then the holder must be
> preempted in kernmode, so we should choose a vcpu in kernmode
> as the most eligible candidate.
>
> For some architecture(e.g. arm/s390), spin/preempt_in_kernel()
> are the same, but they are different for X86.
>
> Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
> ---
> arch/mips/kvm/mips.c | 10 ++++++++++
> arch/powerpc/kvm/powerpc.c | 10 ++++++++++
> arch/s390/kvm/kvm-s390.c | 10 ++++++++++
> arch/x86/kvm/x86.c | 10 ++++++++++
> include/linux/kvm_host.h | 2 ++
> virt/kvm/arm/arm.c | 10 ++++++++++
> virt/kvm/kvm_main.c | 4 ++++
> 7 files changed, 56 insertions(+)
>
> diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> index d4b2ad1..e04e6b3 100644
> --- a/arch/mips/kvm/mips.c
> +++ b/arch/mips/kvm/mips.c
> @@ -98,6 +98,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
> return !!(vcpu->arch.pending_exceptions);
> }
>
> +bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
> +{
> + return false;
> +}
> +
> +bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
> +{
> + return false;
> +}
> +
> int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
> {
> return 1;
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 1a75c0b..c573ddd 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -58,6 +58,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
> return !!(v->arch.pending_exceptions) || kvm_request_pending(v);
> }
>
> +bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
> +{
> + return false;
> +}
> +
> +bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
> +{
> + return false;
> +}
> +
> int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
> {
> return 1;
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index af09d34..f78cdc2 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -2447,6 +2447,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
> return kvm_s390_vcpu_has_irq(vcpu, 0);
> }
>
> +bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
> +{
> + return false;
> +}
> +
> +bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
> +{
> + return false;
> +}
> +
> void kvm_s390_vcpu_block(struct kvm_vcpu *vcpu)
> {
> atomic_or(PROG_BLOCK_SIE, &vcpu->arch.sie_block->prog20);
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 6c97c82..04c6a1f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8435,6 +8435,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
> return kvm_vcpu_running(vcpu) || kvm_vcpu_has_events(vcpu);
> }
>
> +bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
> +{
> + return false;
> +}
> +
> +bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
> +{
> + return false;
> +}
> +
> int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
> {
> return kvm_vcpu_exiting_guest_mode(vcpu) == IN_GUEST_MODE;
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 890b706..9613620 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -798,6 +798,8 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
> void kvm_arch_hardware_unsetup(void);
> void kvm_arch_check_processor_compat(void *rtn);
> int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu);
> +bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu);
> +bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu);
> int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu);
>
> #ifndef __KVM_HAVE_ARCH_VM_ALLOC
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index a39a1e1..e45f780 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -416,6 +416,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
> && !v->arch.power_off && !v->arch.pause);
> }
>
> +bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
> +{
> + return false;
> +}
> +
> +bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
> +{
> + return false;
> +}
Is the differentiation really necessary?
Can't you cache for x86 in all scenarios and simply introduce
kvm_arch_vcpu_in_kernel() ?
Otherwise, we have complexity that might just be avoided (e.g.
kvm_arch_vcpu_spin_in_kernel must only be called on the loaded VCPU)
> +
> /* Just ensure a guest exit from a particular CPU */
> static void exit_vm_noop(void *info)
> {
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index f3f7427..0d0527b 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2324,12 +2324,14 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
> {
> struct kvm *kvm = me->kvm;
> struct kvm_vcpu *vcpu;
> + bool in_kern;
> int last_boosted_vcpu = me->kvm->last_boosted_vcpu;
> int yielded = 0;
> int try = 3;
> int pass;
> int i;
>
> + in_kern = kvm_arch_vcpu_spin_in_kernel(me);
> kvm_vcpu_set_in_spin_loop(me, true);
> /*
> * We boost the priority of a VCPU that is runnable but not
> @@ -2351,6 +2353,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
> continue;
> if (swait_active(&vcpu->wq) && !kvm_arch_vcpu_runnable(vcpu))
> continue;
> + if (in_kern && !kvm_arch_vcpu_preempt_in_kernel(vcpu))
> + continue;
> if (!kvm_vcpu_eligible_for_directed_yield(vcpu))
> continue;
>
>
--
Thanks,
David
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 1/3] KVM: add spinlock-exiting optimize framework
2017-08-07 8:55 ` David Hildenbrand
@ 2017-08-07 9:04 ` Longpeng (Mike)
0 siblings, 0 replies; 11+ messages in thread
From: Longpeng (Mike) @ 2017-08-07 9:04 UTC (permalink / raw)
To: David Hildenbrand
Cc: pbonzini, rkrcmar, agraf, borntraeger, cohuck, christoffer.dall,
marc.zyngier, james.hogan, kvm, linux-kernel, weidong.huang,
arei.gonglei, wangxinxin.wang, longpeng.mike
On 2017/8/7 16:55, David Hildenbrand wrote:
> On 07.08.2017 10:44, Longpeng(Mike) wrote:
>> If the vcpu(me) exit due to request a usermode spinlock, then
>> the spinlock-holder may be preempted in usermode or kernmode.
>>
>> But if the vcpu(me) is in kernmode, then the holder must be
>> preempted in kernmode, so we should choose a vcpu in kernmode
>> as the most eligible candidate.
>>
>> For some architecture(e.g. arm/s390), spin/preempt_in_kernel()
>> are the same, but they are different for X86.
>>
>> Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
>> ---
>> arch/mips/kvm/mips.c | 10 ++++++++++
>> arch/powerpc/kvm/powerpc.c | 10 ++++++++++
>> arch/s390/kvm/kvm-s390.c | 10 ++++++++++
>> arch/x86/kvm/x86.c | 10 ++++++++++
>> include/linux/kvm_host.h | 2 ++
>> virt/kvm/arm/arm.c | 10 ++++++++++
>> virt/kvm/kvm_main.c | 4 ++++
>> 7 files changed, 56 insertions(+)
>>
>> diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
>> index d4b2ad1..e04e6b3 100644
>> --- a/arch/mips/kvm/mips.c
>> +++ b/arch/mips/kvm/mips.c
>> @@ -98,6 +98,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
>> return !!(vcpu->arch.pending_exceptions);
>> }
>>
>> +bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
>> +{
>> + return false;
>> +}
>> +
>> +bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
>> +{
>> + return false;
>> +}
>> +
>> int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
>> {
>> return 1;
>> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
>> index 1a75c0b..c573ddd 100644
>> --- a/arch/powerpc/kvm/powerpc.c
>> +++ b/arch/powerpc/kvm/powerpc.c
>> @@ -58,6 +58,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
>> return !!(v->arch.pending_exceptions) || kvm_request_pending(v);
>> }
>>
>> +bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
>> +{
>> + return false;
>> +}
>> +
>> +bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
>> +{
>> + return false;
>> +}
>> +
>> int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
>> {
>> return 1;
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index af09d34..f78cdc2 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -2447,6 +2447,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
>> return kvm_s390_vcpu_has_irq(vcpu, 0);
>> }
>>
>> +bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
>> +{
>> + return false;
>> +}
>> +
>> +bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
>> +{
>> + return false;
>> +}
>> +
>> void kvm_s390_vcpu_block(struct kvm_vcpu *vcpu)
>> {
>> atomic_or(PROG_BLOCK_SIE, &vcpu->arch.sie_block->prog20);
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 6c97c82..04c6a1f 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -8435,6 +8435,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
>> return kvm_vcpu_running(vcpu) || kvm_vcpu_has_events(vcpu);
>> }
>>
>> +bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
>> +{
>> + return false;
>> +}
>> +
>> +bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
>> +{
>> + return false;
>> +}
>> +
>> int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
>> {
>> return kvm_vcpu_exiting_guest_mode(vcpu) == IN_GUEST_MODE;
>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
>> index 890b706..9613620 100644
>> --- a/include/linux/kvm_host.h
>> +++ b/include/linux/kvm_host.h
>> @@ -798,6 +798,8 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
>> void kvm_arch_hardware_unsetup(void);
>> void kvm_arch_check_processor_compat(void *rtn);
>> int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu);
>> +bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu);
>> +bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu);
>> int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu);
>>
>> #ifndef __KVM_HAVE_ARCH_VM_ALLOC
>> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
>> index a39a1e1..e45f780 100644
>> --- a/virt/kvm/arm/arm.c
>> +++ b/virt/kvm/arm/arm.c
>> @@ -416,6 +416,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
>> && !v->arch.power_off && !v->arch.pause);
>> }
>>
>> +bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
>> +{
>> + return false;
>> +}
>> +
>> +bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
>> +{
>> + return false;
>> +}
>
> Is the differentiation really necessary?
>
> Can't you cache for x86 in all scenarios and simply introduce
> kvm_arch_vcpu_in_kernel() ?
>
For X86 this is necessary, I have no idea how to avoid this, hopes
someone could give me some suggestion. :)
> Otherwise, we have complexity that might just be avoided (e.g.
> kvm_arch_vcpu_spin_in_kernel must only be called on the loaded VCPU)
>
>> +
>> /* Just ensure a guest exit from a particular CPU */
>> static void exit_vm_noop(void *info)
>> {
>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>> index f3f7427..0d0527b 100644
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -2324,12 +2324,14 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
>> {
>> struct kvm *kvm = me->kvm;
>> struct kvm_vcpu *vcpu;
>> + bool in_kern;
>> int last_boosted_vcpu = me->kvm->last_boosted_vcpu;
>> int yielded = 0;
>> int try = 3;
>> int pass;
>> int i;
>>
>> + in_kern = kvm_arch_vcpu_spin_in_kernel(me);
>> kvm_vcpu_set_in_spin_loop(me, true);
>> /*
>> * We boost the priority of a VCPU that is runnable but not
>> @@ -2351,6 +2353,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
>> continue;
>> if (swait_active(&vcpu->wq) && !kvm_arch_vcpu_runnable(vcpu))
>> continue;
>> + if (in_kern && !kvm_arch_vcpu_preempt_in_kernel(vcpu))
>> + continue;
>> if (!kvm_vcpu_eligible_for_directed_yield(vcpu))
>> continue;
>>
>>
>
>
--
Regards,
Longpeng(Mike)
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 2/3] KVM: X86: implement the logic for spinlock optimization
2017-08-07 8:44 ` [PATCH 2/3] KVM: X86: implement the logic for spinlock optimization Longpeng(Mike)
@ 2017-08-07 10:45 ` Paolo Bonzini
2017-08-07 12:28 ` Longpeng(Mike)
0 siblings, 1 reply; 11+ messages in thread
From: Paolo Bonzini @ 2017-08-07 10:45 UTC (permalink / raw)
To: Longpeng(Mike), rkrcmar
Cc: agraf, borntraeger, cohuck, christoffer.dall, marc.zyngier,
james.hogan, kvm, linux-kernel, weidong.huang, arei.gonglei,
wangxinxin.wang, longpeng.mike, david
On 07/08/2017 10:44, Longpeng(Mike) wrote:
> +
> + /*
> + * Intel sdm vol3 ch-25.1.3 says: The “PAUSE-loop exiting”
> + * VM-execution control is ignored if CPL > 0. So the vcpu
> + * is always exiting with CPL=0 if it uses PLE.
This is not true (how can it be?). What 25.1.3 says is, the VCPU is
always at CPL=0 if you get a PAUSE exit (reason 40) and PAUSE exiting is
0 (it always is for KVM). But here you're looking for a VCPU that
didn't get a PAUSE exit, so the CPL can certainly be 3.
However, I understand that vmx_get_cpl can be a bit slow here. You can
actually read SS's access rights directly in this function and get the
DPL from there, that's going to be just a single VMREAD.
The only difference is when vmx->rmode.vm86_active=1. However,
pause-loop exiting is not working properly anyway if
vmx->rmode.vm86_active=1, because CPL=3 according to the processor.
Paolo
> + * The following block needs less cycles than vmx_get_cpl().
> + */
> + if (cpu_has_secondary_exec_ctrls())
> + secondary_exec_ctrl = vmcs_read32(SECONDARY_VM_EXEC_CONTROL);
> + if (secondary_exec_ctrl & SECONDARY_EXEC_PAUSE_LOOP_EXITING)
> + return true;
> +
Paolo
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 2/3] KVM: X86: implement the logic for spinlock optimization
2017-08-07 10:45 ` Paolo Bonzini
@ 2017-08-07 12:28 ` Longpeng(Mike)
2017-08-07 13:16 ` Paolo Bonzini
0 siblings, 1 reply; 11+ messages in thread
From: Longpeng(Mike) @ 2017-08-07 12:28 UTC (permalink / raw)
To: Paolo Bonzini
Cc: Longpeng(Mike),
rkrcmar, agraf, borntraeger, cohuck, christoffer.dall,
marc.zyngier, james.hogan, kvm, linux-kernel, weidong.huang,
arei.gonglei, wangxinxin.wang, david
On 08/07/2017 06:45 PM, Paolo Bonzini wrote:
> On 07/08/2017 10:44, Longpeng(Mike) wrote:
>> +
>> + /*
>> + * Intel sdm vol3 ch-25.1.3 says: The “PAUSE-loop exiting”
>> + * VM-execution control is ignored if CPL > 0. So the vcpu
>> + * is always exiting with CPL=0 if it uses PLE.
>
> This is not true (how can it be?). What 25.1.3 says is, the VCPU is
> always at CPL=0 if you get a PAUSE exit (reason 40) and PAUSE exiting is
> 0 (it always is for KVM). But here you're looking for a VCPU that
> didn't get a PAUSE exit, so the CPL can certainly be 3.
>
Hi Paolo,
My comment above is something wrong(please forgive my poor English), my
origin meaning is:
The “PAUSE-loop exiting” VM-execution control is ignored if
CPL > 0. So the vcpu's CPL is must 0 if it exits due to PLE.
* kvm_arch_spin_in_kernel() returns whether the vcpu(which exits due to
spinlock) is CPL=0. It only be called by kvm_vcpu_on_spin(), and the
input vcpu is 'me' which get a PAUSE exit now. *
I split kvm_arch_vcpu_in_kernel(in RFC) into two functions:
kvm_arch_spin_in_kernel and kvm_arch_preempt_in_kernel
Because of KVM/VMX L1 never set CPU_BASED_PAUSE_EXITING and only set
SECONDARY_EXEC_PAUSE_LOOP_EXITING if supported, so for L1:
1. get a PAUSE exit with CPL=0 if PLE is supported
2. never get a PAUSE exit if don't support PLE
So, I think it can direct return true(CPL=0) if supports PLE.
But for nested KVM/VMX(I'm not familiar with nested), it could set
CPU_BASED_PAUSE_EXITING, so I think get_cpl() is also needed.
If the above is correct, what about this way( we can save a vmcs_read
opeartion for L1):
kvm_arch_vcpu_spin_in_kernel(vcpu)
{
if (!is_guest_mode(vcpu))
return true;
return vmx_get_cpl(vcpu) == 0;
}
kvm_vcpu_on_spin()
{
/* @me get a PAUSE exit */
me_in_kernel = kvm_arch_vcpu_spin_in_kernel(me);
...
for each vcpu {
...
if (me_in_kernel && !...preempt_in_kernel(vcpu))
continue;
...
}
...
}
---
Regards,
Longpeng(Mike)
> However, I understand that vmx_get_cpl can be a bit slow here. You can
> actually read SS's access rights directly in this function and get the
> DPL from there, that's going to be just a single VMREAD.
>
> The only difference is when vmx->rmode.vm86_active=1. However,
> pause-loop exiting is not working properly anyway if
> vmx->rmode.vm86_active=1, because CPL=3 according to the processor.
>
> Paolo
>
>> + * The following block needs less cycles than vmx_get_cpl().
>> + */
>> + if (cpu_has_secondary_exec_ctrls())
>> + secondary_exec_ctrl = vmcs_read32(SECONDARY_VM_EXEC_CONTROL);
>> + if (secondary_exec_ctrl & SECONDARY_EXEC_PAUSE_LOOP_EXITING)
>> + return true;
>> +
>
> Paolo
>
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 2/3] KVM: X86: implement the logic for spinlock optimization
2017-08-07 12:28 ` Longpeng(Mike)
@ 2017-08-07 13:16 ` Paolo Bonzini
0 siblings, 0 replies; 11+ messages in thread
From: Paolo Bonzini @ 2017-08-07 13:16 UTC (permalink / raw)
To: Longpeng(Mike)
Cc: Longpeng(Mike),
rkrcmar, agraf, borntraeger, cohuck, christoffer.dall,
marc.zyngier, james.hogan, kvm, linux-kernel, weidong.huang,
arei.gonglei, wangxinxin.wang, david
On 07/08/2017 14:28, Longpeng(Mike) wrote:
> * kvm_arch_spin_in_kernel() returns whether the vcpu (which exits due to
> spinlock) is CPL=0. It only be called by kvm_vcpu_on_spin(), and the
> input vcpu is 'me' which get a PAUSE exit now. *
>
> I split kvm_arch_vcpu_in_kernel(in RFC) into two functions:
> kvm_arch_spin_in_kernel and kvm_arch_preempt_in_kernel
>
> Because of KVM/VMX L1 never set CPU_BASED_PAUSE_EXITING and only set
> SECONDARY_EXEC_PAUSE_LOOP_EXITING if supported, so for L1:
I understand better now. I think vmx.c should just return true from
vmx_spin_in_kernel. However, kvm_arch_vcpu_spin_in_kernel is not
necessary. Instead you should make "in_kern" an argument to
kvm_vcpu_on_spin (maybe renamed to "yield_to_kernel_mode_vcpu").
Then vmx.c can just call "kvm_vcpu_on_spin(vcpu, true)".
> 1. get a PAUSE exit with CPL=0 if PLE is supported
> 2. never get a PAUSE exit if don't support PLE
>
> So, I think it can direct return true(CPL=0) if supports PLE.
>
> But for nested KVM/VMX(I'm not familiar with nested), it could set
> CPU_BASED_PAUSE_EXITING, so I think get_cpl() is also needed.
If the nested hypervisor sets CPU_BASED_PAUSE_EXITING, a PAUSE vmexit
while running a nested guest would be reflected to the nested
hypervisor. So you wouldn't get to handle_pause and thus to
kvm_vcpu_on_spin.
Thanks,
Paolo
^ permalink raw reply [flat|nested] 11+ messages in thread
end of thread, other threads:[~2017-08-07 13:16 UTC | newest]
Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2017-08-07 8:44 [PATCH 0/3] KVM: optimize the kvm_vcpu_on_spin Longpeng(Mike)
2017-08-07 8:44 ` [PATCH 1/3] KVM: add spinlock-exiting optimize framework Longpeng(Mike)
2017-08-07 8:55 ` David Hildenbrand
2017-08-07 9:04 ` Longpeng (Mike)
2017-08-07 8:44 ` [PATCH 2/3] KVM: X86: implement the logic for spinlock optimization Longpeng(Mike)
2017-08-07 10:45 ` Paolo Bonzini
2017-08-07 12:28 ` Longpeng(Mike)
2017-08-07 13:16 ` Paolo Bonzini
2017-08-07 8:44 ` [PATCH 3/3] KVM: implement spinlock optimization logic for arm/s390 Longpeng(Mike)
2017-08-07 8:52 ` David Hildenbrand
2017-08-07 8:54 ` Longpeng (Mike)
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