linux-kernel - Re: [PATCH v2 0/4] KVM: Paravirt remote TLB flush

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Message-ID: <CANRm+Cw3Lj08tkAJ8+uVSXkTsMpghwC1T9M8MYXJtfynGrNsGg@mail.gmail.com>
Date:   Fri, 10 Nov 2017 15:11:02 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH v2 0/4] KVM: Paravirt remote TLB flush

2017-11-10 15:04 GMT+08:00 Wanpeng Li <kernellwp@...il.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. Idea was discussed here:
> https://lkml.org/lkml/2012/2/20/157
>
> 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.
>
> In addition, thanks for commit 9e52fc2b50d ("x86/mm: Enable RCU based
> page table freeing (CONFIG_HAVE_RCU_TABLE_FREE=y)")
>
> 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%

v1 -> v2:
 * a new CPUID feature bit
 * fix cmpxchg check
 * use kvm_vcpu_flush_tlb() to get the statistics right
 * just OR the KVM_VCPU_PREEMPTED in kvm_steal_time_set_preempted
 * add a new bool argument to kvm_x86_ops->tlb_flush
 * __cpumask_clear_cpu() instead of cpumask_clear_cpu()
 * not put cpumask_t on stack
 * rebase the patchset against "locking/qspinlock/x86: Avoid
test-and-set when PV_DEDICATED is set" v3

>
> Wanpeng Li (4):
>   KVM: Add vCPU running/preempted state
>   KVM: Add paravirt remote TLB flush
>   KVM: X86: introduce invalidate_gpa argument to tlb flush
>   KVM: Add flush_on_enter before guest enter
>
>  Documentation/virtual/kvm/cpuid.txt  | 10 ++++++++++
>  arch/x86/include/asm/kvm_host.h      |  2 +-
>  arch/x86/include/uapi/asm/kvm_para.h |  6 ++++++
>  arch/x86/kernel/kvm.c                | 35 ++++++++++++++++++++++++++++++++++-
>  arch/x86/kvm/cpuid.c                 |  3 ++-
>  arch/x86/kvm/svm.c                   | 14 +++++++-------
>  arch/x86/kvm/vmx.c                   | 21 +++++++++++----------
>  arch/x86/kvm/x86.c                   | 24 +++++++++++++++---------
>  8 files changed, 86 insertions(+), 29 deletions(-)
>
> --
> 2.7.4
>