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SubjectRe: [PATCH v2 2/4] KVM: Add paravirt remote TLB flush
2017-11-10 16:33 GMT+08:00 Wanpeng Li <kernellwp@gmail.com>:
> 2017-11-10 16:24 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>> 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?
>
> Yeah, I just complete v3 according to Peterz's comments in another
> guy's thread, I will send out them after completing the testing.

This is how it looks it. https://pastebin.com/raw/L2vqu4cZ

Regards,
Wanpeng Li

>
> Regards,
> Wanpeng Li
>
>>
>> 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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