* [PATCH] x86/kvm: Don't use pv tlb/ipi/sched_yield if on 1 vCPU
@ 2022-02-18 8:10 Wanpeng Li
2022-02-18 8:36 ` Paolo Bonzini
0 siblings, 1 reply; 2+ messages in thread
From: Wanpeng Li @ 2022-02-18 8:10 UTC (permalink / raw)
To: linux-kernel, kvm
Cc: Paolo Bonzini, Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li,
Jim Mattson, Joerg Roedel
From: Wanpeng Li <wanpengli@tencent.com>
Inspired by commit 3553ae5690a (x86/kvm: Don't use pvqspinlock code if
only 1 vCPU), on a VM with only 1 vCPU, there is no need to enable
pv tlb/ipi/sched_yield and we can save the memory for __pv_cpu_mask.
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
arch/x86/kernel/kvm.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index a438217cbfac..f734e3b0cfec 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -462,19 +462,22 @@ static bool pv_tlb_flush_supported(void)
{
return (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) &&
!kvm_para_has_hint(KVM_HINTS_REALTIME) &&
- kvm_para_has_feature(KVM_FEATURE_STEAL_TIME));
+ kvm_para_has_feature(KVM_FEATURE_STEAL_TIME) &&
+ (num_possible_cpus() != 1));
}
static bool pv_ipi_supported(void)
{
- return kvm_para_has_feature(KVM_FEATURE_PV_SEND_IPI);
+ return (kvm_para_has_feature(KVM_FEATURE_PV_SEND_IPI) &&
+ (num_possible_cpus() != 1));
}
static bool pv_sched_yield_supported(void)
{
return (kvm_para_has_feature(KVM_FEATURE_PV_SCHED_YIELD) &&
!kvm_para_has_hint(KVM_HINTS_REALTIME) &&
- kvm_para_has_feature(KVM_FEATURE_STEAL_TIME));
+ kvm_para_has_feature(KVM_FEATURE_STEAL_TIME) &&
+ (num_possible_cpus() != 1));
}
#define KVM_IPI_CLUSTER_SIZE (2 * BITS_PER_LONG)
--
2.25.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] x86/kvm: Don't use pv tlb/ipi/sched_yield if on 1 vCPU
2022-02-18 8:10 [PATCH] x86/kvm: Don't use pv tlb/ipi/sched_yield if on 1 vCPU Wanpeng Li
@ 2022-02-18 8:36 ` Paolo Bonzini
0 siblings, 0 replies; 2+ messages in thread
From: Paolo Bonzini @ 2022-02-18 8:36 UTC (permalink / raw)
To: Wanpeng Li, linux-kernel, kvm
Cc: Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
Joerg Roedel
On 2/18/22 09:10, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
>
> Inspired by commit 3553ae5690a (x86/kvm: Don't use pvqspinlock code if
> only 1 vCPU), on a VM with only 1 vCPU, there is no need to enable
> pv tlb/ipi/sched_yield and we can save the memory for __pv_cpu_mask.
>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> arch/x86/kernel/kvm.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index a438217cbfac..f734e3b0cfec 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -462,19 +462,22 @@ static bool pv_tlb_flush_supported(void)
> {
> return (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) &&
> !kvm_para_has_hint(KVM_HINTS_REALTIME) &&
> - kvm_para_has_feature(KVM_FEATURE_STEAL_TIME));
> + kvm_para_has_feature(KVM_FEATURE_STEAL_TIME) &&
> + (num_possible_cpus() != 1));
> }
>
> static bool pv_ipi_supported(void)
> {
> - return kvm_para_has_feature(KVM_FEATURE_PV_SEND_IPI);
> + return (kvm_para_has_feature(KVM_FEATURE_PV_SEND_IPI) &&
> + (num_possible_cpus() != 1));
> }
>
> static bool pv_sched_yield_supported(void)
> {
> return (kvm_para_has_feature(KVM_FEATURE_PV_SCHED_YIELD) &&
> !kvm_para_has_hint(KVM_HINTS_REALTIME) &&
> - kvm_para_has_feature(KVM_FEATURE_STEAL_TIME));
> + kvm_para_has_feature(KVM_FEATURE_STEAL_TIME) &&
> + (num_possible_cpus() != 1));
> }
>
> #define KVM_IPI_CLUSTER_SIZE (2 * BITS_PER_LONG)
Queued, thanks.
Paolo
^ permalink raw reply [flat|nested] 2+ messages in thread
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