linux-kernel - [PATCH v4 0/4] KVM: X86: Paravirt remote TLB flush

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Date:   Sat, 11 Nov 2017 19:18:37 -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 v4 0/4] KVM: X86: 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       297.5% 
24 vCPUs        1109        3871       249%
32 vCPUs        1025        3375       229.3% 

Note: The patchset is rebased against "locking/qspinlock/x86: Avoid
   test-and-set when PV_DEDICATED is set" v3

v3 -> v4:
 * use READ_ONCE()
 * use try_cmpxchg instead of cmpxchg
 * add {} to if
 * no FLUSH flags to preserve during set_preempted
 * "KVM: X86" prefix to patch subject

v2 -> v3: 
 * percpu cpumask

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: X86: Add vCPU running/preempted state
  KVM: X86: Add paravirt remote TLB flush
  KVM: X86: introduce invalidate_gpa argument to tlb flush
  KVM: X86: Add flush_on_enter before guest enter

 Documentation/virtual/kvm/cpuid.txt  |  4 ++++
 arch/x86/include/asm/kvm_host.h      |  2 +-
 arch/x86/include/uapi/asm/kvm_para.h |  6 +++++
 arch/x86/kernel/kvm.c                | 46 ++++++++++++++++++++++++++++++++++--
 arch/x86/kvm/cpuid.c                 |  3 ++-
 arch/x86/kvm/svm.c                   | 14 +++++------
 arch/x86/kvm/vmx.c                   | 21 ++++++++--------
 arch/x86/kvm/x86.c                   | 25 +++++++++++++-------
 8 files changed, 88 insertions(+), 30 deletions(-)

-- 
2.7.4