Re: [PATCH] x86/kvm: Don't use pv tlb/ipi/sched_yield if on 1 vCPU

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On 2/18/22 09:10, Wanpeng Li wrote:
From: Wanpeng Li <wanpengli@xxxxxxxxxxx>

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@xxxxxxxxxxx>
---
  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




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