On 09/11/2017 03:02, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> ---
> arch/x86/include/uapi/asm/kvm_para.h | 1 +
> arch/x86/kernel/kvm.c | 29 +++++++++++++++++++++++++++++
> 2 files changed, 30 insertions(+)
>
> diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
> index ff23ce9..189e354 100644
> --- a/arch/x86/include/uapi/asm/kvm_para.h
> +++ b/arch/x86/include/uapi/asm/kvm_para.h
> @@ -52,6 +52,7 @@ 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 1b1b641..2e2f3ae 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 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_t flushmask;
> +
> +
> + 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 | 1 <<
> + KVM_VCPU_SHOULD_FLUSH))
> + cpumask_clear_cpu(cpu, &flushmask);
> + }
> + }
> +
> + native_flush_tlb_others(&flushmask, info);
> +}
> +
> void __init kvm_guest_init(void)
> {
> int i;
> @@ -484,6 +511,8 @@ void __init kvm_guest_init(void)
> pv_time_ops.steal_clock = kvm_steal_clock;
> }
>
> + pv_mmu_ops.flush_tlb_others = kvm_flush_tlb_others;
This needs to be keyed on a new CPUID feature bit. Eduardo is also
adding a new "PV_DEDICATED" hint and you might disable PV TLB flush when
PV_DEDICATED is set.
Paolo
> if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
> apic_set_eoi_write(kvm_guest_apic_eoi_write);
>
>
