linux-kernel - [PATCH v5 0/2] x86/kvm: Reduce vcpu_is

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Date:   Mon, 20 Feb 2017 13:36:02 -0500
From:   Waiman Long <longman@...hat.com>
To:     Jeremy Fitzhardinge <jeremy@...p.org>,
        Chris Wright <chrisw@...s-sol.org>,
        Alok Kataria <akataria@...are.com>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     linux-arch@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        xen-devel@...ts.xenproject.org, kvm@...r.kernel.org,
        Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH v5 0/2] x86/kvm: Reduce vcpu_is_preempted() overhead

 v4->v5:
  - As suggested by PeterZ, use the asm-offsets header file generation
    mechanism to get the offset of the preempted field in
    kvm_steal_time instead of hardcoding it.

 v3->v4:
  - Fix x86-32 build error.

 v2->v3:
  - Provide an optimized __raw_callee_save___kvm_vcpu_is_preempted()
    in assembly as suggested by PeterZ.
  - Add a new patch to change vcpu_is_preempted() argument type to long
    to ease the writing of the assembly code.

 v1->v2:
  - Rerun the fio test on a different system on both bare-metal and a
    KVM guest. Both sockets were utilized in this test.
  - The commit log was updated with new performance numbers, but the
    patch wasn't changed.
  - Drop patch 2.

As it was found that the overhead of callee-save vcpu_is_preempted()
can have some impact on system performance on a VM guest, especially
of x86-64 guest, this patch set intends to reduce this performance
overhead by replacing the C __kvm_vcpu_is_preempted() function by
an optimized version of __raw_callee_save___kvm_vcpu_is_preempted()
written in assembly.

Waiman Long (2):
  x86/paravirt: Change vcp_is_preempted() arg type to long
  x86/kvm: Provide optimized version of vcpu_is_preempted() for x86-64

 arch/x86/include/asm/paravirt.h      |  2 +-
 arch/x86/include/asm/qspinlock.h     |  2 +-
 arch/x86/kernel/asm-offsets_64.c     |  9 +++++++++
 arch/x86/kernel/kvm.c                | 26 +++++++++++++++++++++++++-
 arch/x86/kernel/paravirt-spinlocks.c |  2 +-
 5 files changed, 37 insertions(+), 4 deletions(-)

-- 
1.8.3.1