On Wed, Jan 08, 2020 at 09:50:01AM +0800, Wanpeng Li wrote: > From: Wanpeng Li <wanpengli@xxxxxxxxxxx> > > To deliver all of the resources of a server to instances in cloud, there are no > housekeeping cpus reserved. libvirtd, qemu main loop, kthreads, and other agent/tools > etc which can't be offloaded to other hardware like smart nic, these stuff will > contend with vCPUs even if MWAIT/HLT instructions executed in the guest. > > The is no trap and yield the pCPU after we expose mwait/hlt to the guest [1][2], > the top command on host still observe 100% cpu utilization since qemu process is > running even though guest who has the power management capability executes mwait. > Actually we can observe the physical cpu has already enter deeper cstate by > powertop on host. > > For virtualization, there is a HLT activity state in CPU VMCS field which indicates > the logical processor is inactive because it executed the HLT instruction, but > SDM 24.4.2 mentioned that execution of the MWAIT instruction may put a logical > processor into an inactive state, however, this VMCS field never reflects this > state. So far I think I can follow, however it does not explain who consumes this VMCS state if it is set and how that helps. Also, this: > This patch avoids fine granularity intercept and reschedule vCPU if MWAIT/HLT > instructions executed, because it can worse the message-passing workloads which > will switch between idle and running frequently in the guest. Lets penalty the > vCPU which is long idle through tick-based sampling and preemption. is just complete gibberish. And I have no idea what problem you're trying to solve how. Also, I don't think the TSC/MPERF ratio is architected, we can't assume this is true for everything that has APERFMPERF. /me tries to reconstruct intent from patch So what you're doing is, mark the CPU 'idle' when the MPERF/TSC ratio < 1%, and then frob the vruntime such that it will hopefully preempt. That's pretty disgusting. Please, write a coherent problem statement and justify the magic choices. This is unreviewable.
