Hi
This patchset attemps to introduce a new pv feature, lazy tscdeadline.
Everytime guest write msr of MSR_IA32_TSC_DEADLINE, a vm-exit occurs
and host side handle it. However, a lot of the vm-exit is unnecessary
because the timer is often over-written before it expires.
v : write to msr of tsc deadline
| : timer armed by tsc deadline
v v v v v | | | | |
---------------------------------------> Time
The timer armed by msr write is over-written before expires and the
vm-exit caused by it are wasted. The lazy tscdeadline works as following,
v v v v v | |
---------------------------------------> Time
'- arm -'
The 1st timer is responsible for arming the next timer. When the armed
timer is expired, it will check pending and arm a new timer.
In the netperf test with TCP_RR on loopback, this lazy_tscdeadline can
reduce vm-exit obviously.
Close Open
--------------------------------------------------------
VM-Exit
sum 12617503 5815737
intr 0% 37023 0% 33002
cpuid 0% 1 0% 0
halt 19% 2503932 47% 2780683
msr-write 79% 10046340 51% 2966824
pause 0% 90 0% 84
ept-violation 0% 584 0% 336
ept-misconfig 0% 0 0% 2
preemption-timer 0% 29518 0% 34800
-------------------------------------------------------
MSR-Write
sum 10046455 2966864
apic-icr 25% 2533498 93% 2781235
tsc-deadline 74% 7512945 6% 185629
This patchset is made and tested on 6.4.0, includes 4 patches,
The 1st one adds necessary data structures for this feature
The 2nd one adds the specific msr operations between guest and host
The 3rd one are the one make this feature works.
The 4th one adds debugfs file into /sys/kernel/debug/kvm for this feature
Changes from V1:
- In 3rd patch, rename the variable of kvm_host_lazy_tscdeadline from 'host'
to 'hlt'. And in addition, add more details into the comment of patch
- Add 4th patch which add debugfs file for this patch
Any comment is welcome.
Thanks
Jianchao
Wang Jianchao (4)
KVM: x86: add msr register and data structure for lazy tscdeadline
KVM: x86: exchange info about lazy_tscdeadline with msr
KVM: X86: add lazy tscdeadline support to reduce vm-exit of msr-write
KVM: x86: add debugfs file for lazy tscdeadline
arch/x86/include/asm/kvm_host.h | 10 +++
arch/x86/include/uapi/asm/kvm_para.h | 9 +++
arch/x86/kernel/apic/apic.c | 47 ++++++++++++-
arch/x86/kernel/kvm.c | 13 ++++
arch/x86/kvm/cpuid.c | 1 +
arch/x86/kvm/debugfs.c | 79 ++++++++++++++++++++-
arch/x86/kvm/lapic.c | 129 ++++++++++++++++++++++++++++++++---
arch/x86/kvm/lapic.h | 4 ++
arch/x86/kvm/x86.c | 26 +++++++
9 files changed, 308 insertions(+), 10 deletions(-)
