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

Zhimin Feng
2021-02-06T00:52:58Z

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