Re: [PATCH] kvm: rename HINTS_DEDICATED to KVM_HINTS_REALTIME

Paolo Bonzini
2018-05-17T16:05:51Z

On 17/05/2018 16:54, Michael S. Tsirkin wrote:
> HINTS_DEDICATED seems to be somewhat confusing:
>
> Guest doesn't really care whether it's the only task running on a host
> CPU as long as it's not preempted.
>
> And there are more reasons for Guest to be preempted than host CPU
> sharing, for example, with memory overcommit it can get preempted on a
> memory access, post copy migration can cause preemption, etc.
>
> Let's call it KVM_HINTS_REALTIME which seems to better
> match what guests expect.
>
> Also, the flag most be set on all vCPUs - current guests assume this.
> Note so in the documentation.
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> Documentation/virtual/kvm/cpuid.txt | 6 +++---
> arch/x86/include/uapi/asm/kvm_para.h | 2 +-
> arch/x86/kernel/kvm.c | 8 ++++----
> 3 files changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt
> index d4f33eb8..ab022dc 100644
> --- a/Documentation/virtual/kvm/cpuid.txt
> +++ b/Documentation/virtual/kvm/cpuid.txt
> @@ -72,8 +72,8 @@ KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side
>
> flag || value || meaning
> ==================================================================================
> -KVM_HINTS_DEDICATED || 0 || guest checks this feature bit to
> - || || determine if there is vCPU pinning
> - || || and there is no vCPU over-commitment,
> +KVM_HINTS_REALTIME || 0 || guest checks this feature bit to
> + || || determine that vCPUs are never
> + || || preempted for an unlimited time,
> || || allowing optimizations
> ----------------------------------------------------------------------------------
> diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
> index 4c851eb..0ede697 100644
> --- a/arch/x86/include/uapi/asm/kvm_para.h
> +++ b/arch/x86/include/uapi/asm/kvm_para.h
> @@ -29,7 +29,7 @@
> #define KVM_FEATURE_PV_TLB_FLUSH 9
> #define KVM_FEATURE_ASYNC_PF_VMEXIT 10
>
> -#define KVM_HINTS_DEDICATED 0
> +#define KVM_HINTS_REALTIME 0
>
> /* The last 8 bits are used to indicate how to interpret the flags field
> * in pvclock structure. If no bits are set, all flags are ignored.
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 7867417..5b2300b 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -457,7 +457,7 @@ static void __init sev_map_percpu_data(void)
> static void __init kvm_smp_prepare_cpus(unsigned int max_cpus)
> {
> native_smp_prepare_cpus(max_cpus);
> - if (kvm_para_has_hint(KVM_HINTS_DEDICATED))
> + if (kvm_para_has_hint(KVM_HINTS_REALTIME))
> static_branch_disable(&virt_spin_lock_key);
> }
>
> @@ -553,7 +553,7 @@ static void __init kvm_guest_init(void)
> }
>
> if (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) &&
> - !kvm_para_has_hint(KVM_HINTS_DEDICATED) &&
> + !kvm_para_has_hint(KVM_HINTS_REALTIME) &&
> kvm_para_has_feature(KVM_FEATURE_STEAL_TIME))
> pv_mmu_ops.flush_tlb_others = kvm_flush_tlb_others;
>
> @@ -649,7 +649,7 @@ static __init int kvm_setup_pv_tlb_flush(void)
> int cpu;
>
> if (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) &&
> - !kvm_para_has_hint(KVM_HINTS_DEDICATED) &&
> + !kvm_para_has_hint(KVM_HINTS_REALTIME) &&
> kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
> for_each_possible_cpu(cpu) {
> zalloc_cpumask_var_node(per_cpu_ptr(&__pv_tlb_mask, cpu),
> @@ -745,7 +745,7 @@ void __init kvm_spinlock_init(void)
> if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
> return;
>
> - if (kvm_para_has_hint(KVM_HINTS_DEDICATED))
> + if (kvm_para_has_hint(KVM_HINTS_REALTIME))
> return;
>
> __pv_init_lock_hash();
>

Queued, thanks.

Paolo