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SubjectRe: [PATCH] x86/kvm: Don't use pvqspinlock code if only 1 vCPU
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On 17/07/2018 23:59, Waiman Long wrote:
> On a VM with only 1 vCPU, the locking fast path will always be
> successful. In this case, there is no need to use the the PV qspinlock
> code which has higher overhead on the unlock side than the native
> qspinlock code.
>
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
> arch/x86/kernel/kvm.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 5b2300b..575c9a5 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -748,6 +748,10 @@ void __init kvm_spinlock_init(void)
> if (kvm_para_has_hint(KVM_HINTS_REALTIME))
> return;
>
> + /* Don't use the pvqspinlock code if there is only 1 vCPU. */
> + if (num_possible_cpus() == 1)
> + return;
> +
> __pv_init_lock_hash();
> pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
> pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
>

Queued, thanks.

Paolo

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