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SubjectRe: [PATCH v2 2/4] KVM: Add paravirt remote TLB flush
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On 10/11/2017 08:04, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@hotmail.com>
>
> Remote flushing api's does a busy wait which is fine in bare-metal
> scenario. But with-in the guest, the vcpus might have been pre-empted
> or blocked. In this scenario, the initator vcpu would end up
> busy-waiting for a long amount of time.
>
> This patch set implements para-virt flush tlbs making sure that it
> does not wait for vcpus that are sleeping. And all the sleeping vcpus
> flush the tlb on guest enter.
>
> The best result is achieved when we're overcommiting the host by running
> multiple vCPUs on each pCPU. In this case PV tlb flush avoids touching
> vCPUs which are not scheduled and avoid the wait on the main CPU.
>
> Test on a Haswell i7 desktop 4 cores (2HT), so 8 pCPUs, running ebizzy in
> one linux guest.
>
> ebizzy -M
> vanilla optimized boost
> 8 vCPUs 10152 10083 -0.68%
> 16 vCPUs 1224 4866 297.5%
> 24 vCPUs 1109 3871 249%
> 32 vCPUs 1025 3375 229.3%
>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
> ---
> Documentation/virtual/kvm/cpuid.txt | 4 ++++
> arch/x86/include/uapi/asm/kvm_para.h | 2 ++
> arch/x86/kernel/kvm.c | 31 +++++++++++++++++++++++++++++++
> 3 files changed, 37 insertions(+)
>
> diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt
> index 117066a..9693fcc 100644
> --- a/Documentation/virtual/kvm/cpuid.txt
> +++ b/Documentation/virtual/kvm/cpuid.txt
> @@ -60,6 +60,10 @@ KVM_FEATURE_PV_DEDICATED || 8 || guest checks this feature bit
> || || mizations such as usage of
> || || qspinlocks.
> ------------------------------------------------------------------------------
> +KVM_FEATURE_PV_TLB_FLUSH || 9 || guest checks this feature bit
> + || || before enabling paravirtualized
> + || || tlb flush.
> +------------------------------------------------------------------------------
> KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side
> || || per-cpu warps are expected in
> || || kvmclock.
> diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
> index 9ead1ed..a028479 100644
> --- a/arch/x86/include/uapi/asm/kvm_para.h
> +++ b/arch/x86/include/uapi/asm/kvm_para.h
> @@ -25,6 +25,7 @@
> #define KVM_FEATURE_PV_EOI 6
> #define KVM_FEATURE_PV_UNHALT 7
> #define KVM_FEATURE_PV_DEDICATED 8
> +#define KVM_FEATURE_PV_TLB_FLUSH 9
>
> /* 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.
> @@ -53,6 +54,7 @@ struct kvm_steal_time {
>
> #define KVM_VCPU_NOT_PREEMPTED (0 << 0)
> #define KVM_VCPU_PREEMPTED (1 << 0)
> +#define KVM_VCPU_SHOULD_FLUSH (1 << 1)
>
> #define KVM_CLOCK_PAIRING_WALLCLOCK 0
> struct kvm_clock_pairing {
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 66ed3bc..50f4b6a 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -465,6 +465,33 @@ static void __init kvm_apf_trap_init(void)
> update_intr_gate(X86_TRAP_PF, async_page_fault);
> }
>
> +static cpumask_t flushmask;

Hi Wanpeng,

are you going to send v3 with a percpu variable?

Paolo

> +static void kvm_flush_tlb_others(const struct cpumask *cpumask,
> + const struct flush_tlb_info *info)
> +{
> + u8 state;
> + int cpu;
> + struct kvm_steal_time *src;
> +
> + cpumask_copy(&flushmask, cpumask);
> + /*
> + * We have to call flush only on online vCPUs. And
> + * queue flush_on_enter for pre-empted vCPUs
> + */
> + for_each_cpu(cpu, cpumask) {
> + src = &per_cpu(steal_time, cpu);
> + state = src->preempted;
> + if ((state & KVM_VCPU_PREEMPTED)) {
> + if (cmpxchg(&src->preempted, state, state |
> + KVM_VCPU_SHOULD_FLUSH) == state)
> + __cpumask_clear_cpu(cpu, &flushmask);
> + }
> + }
> +
> + native_flush_tlb_others(&flushmask, info);
> +}
> +
> void __init kvm_guest_init(void)
> {
> int i;
> @@ -484,6 +511,10 @@ void __init kvm_guest_init(void)
> pv_time_ops.steal_clock = kvm_steal_clock;
> }
>
> + if (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) &&
> + !kvm_para_has_feature(KVM_FEATURE_PV_DEDICATED))
> + pv_mmu_ops.flush_tlb_others = kvm_flush_tlb_others;
> +
> if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
> apic_set_eoi_write(kvm_guest_apic_eoi_write);
>
>

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