2017-11-09 18:48 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>:
> 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
Will do.
> adding a new "PV_DEDICATED" hint and you might disable PV TLB flush when
> PV_DEDICATED is set.
Why disable PV TLB flush for PV_DEDICATED(qspinlock)?
Regards,
Wanpeng Li
