linux-kernel - [RESEND RFC: timer passthrough 0/9] Support timer passthrough for VM

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Date:   Fri,  5 Feb 2021 18:03:08 +0800
From:   Zhimin Feng <fengzhimin@...edance.com>
To:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     pbonzini@...hat.com, seanjc@...gle.com, vkuznets@...hat.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        fweisbec@...il.com, zhouyibo@...edance.com,
        zhanghaozhong@...edance.com, Zhimin Feng <fengzhimin@...edance.com>
Subject: [RESEND RFC: timer passthrough 0/9] Support timer passthrough for VM

The main motivation for this patch is to improve the performance of VM.
This patch series introduces how to enable the timer passthrough in
non-root mode.

The main idea is to offload the host timer to the preemtion timer in
non-root mode. Through doing this, guest can write tscdeadline msr directly
in non-root mode and host timer isn't lost. If CPU is in root mode,
guest timer is switched to software timer.

Testing on Intel(R) Xeon(R) Platinum 8260 server.

The guest OS is Debian(kernel: 4.19.28). The specific configuration is
 is as follows: 8 cpu, 16GB memory, guest idle=poll
memcached in guest(memcached -d -t 8 -u root)

I use the memtier_benchmark tool to test performance
(memtier_benchmark -P memcache_text -s guest_ip -c 16 -t 32
 --key-maximum=10000000000 --random-data --data-size-range=64-128 -p 11211
 --generate-keys --ratio 5:1 --test-time=500)

Total Ops can be improved 25% and Avg.Latency can be improved 20% when
the timer-passthrough is enabled.

=============================================================
               | Enable timer-passth | Disable timer-passth |
=============================================================
Totals Ops/sec |    514869.67        |     411766.67        |
-------------------------------------------------------------
Avg.Latency    |    0.99483          |     1.24294          |
=============================================================


Zhimin Feng (9):
  KVM: vmx: hook set_next_event for getting the host tscd
  KVM: vmx: enable host lapic timer offload preemtion timer
  KVM: vmx: enable passthrough timer to guest
  KVM: vmx: enable passth timer switch to sw timer
  KVM: vmx: use tsc_adjust to enable tsc_offset timer passthrough
  KVM: vmx: check enable_timer_passth strictly
  KVM: vmx: save the initial value of host tscd
  KVM: vmx: Dynamically open or close the timer-passthrough for pre-vm
  KVM: vmx: query the state of timer-passth for vm

 arch/x86/include/asm/kvm_host.h |  27 ++++
 arch/x86/kvm/lapic.c            |   1 +
 arch/x86/kvm/vmx/vmx.c          | 331 +++++++++++++++++++++++++++++++++++++++-
 arch/x86/kvm/x86.c              |  26 +++-
 include/linux/kvm_host.h        |   1 +
 include/uapi/linux/kvm.h        |   3 +
 kernel/time/tick-common.c       |   1 +
 tools/include/uapi/linux/kvm.h  |   3 +
 virt/kvm/kvm_main.c             |   1 +
 9 files changed, 389 insertions(+), 5 deletions(-)

-- 
2.11.0