On Fri, Feb 05, 2021 at 06:03:08PM +0800, Zhimin Feng wrote: > 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. Nice! Those are impressive numbers! > > 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. I am sorry - but I am having a hard time understanding the sentence above so let me ask some specific questions. - How do you protect against the guest DoS-ing the host and mucking with the host timer? - As in can you explain how the host can still continue scheduling it's own quanta? And one more - what happens with Live Migration? I would assume that becomes a no-go anymore unless you swap in the guest timer back in? So we end up emulating the MSR again? Thanks! > > 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 >
