linux-kernel - [PATCH 0/3] KVM: Paravirt remote TLB flush

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Date:   Wed,  8 Nov 2017 17:52:12 -0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: [PATCH 0/3] KVM: Paravirt remote TLB flush

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       397.5% 
24 vCPUs        1109        3871       349%
32 vCPUs        1025        3375       329% 

Wanpeng Li (3):
  KVM: Add vCPU running/preempted state
  KVM: Add paravirt remote TLB flush
  KVM: Add flush_on_enter before guest enter

 arch/x86/include/uapi/asm/kvm_para.h |  4 ++++
 arch/x86/kernel/kvm.c                | 31 ++++++++++++++++++++++++++++++-
 arch/x86/kvm/x86.c                   | 12 ++++++++++--
 3 files changed, 44 insertions(+), 3 deletions(-)

-- 
2.7.4