Re: [PATCH] KVM: Disable wake-affine vCPU process to mitigate lock holder preemption

From: Christophe de Dinechin
Date: Fri Aug 02 2019 - 04:30:24 EST

Dario Faggioli writes:

> On Tue, 2019-07-30 at 17:33 +0800, Wanpeng Li wrote:
>> However, in multiple VMs over-subscribe virtualization scenario, it
>> increases
>> the probability to incur vCPU stacking which means that the sibling
>> vCPUs from
>> the same VM will be stacked on one pCPU. I test three 80 vCPUs VMs
>> running on
>> one 80 pCPUs Skylake server(PLE is supported), the ebizzy score can
>> increase 17%
>> after disabling wake-affine for vCPU process.
> Can't we achieve this by removing SD_WAKE_AFFINE from the relevant
> scheduling domains? By acting on
> /proc/sys/kernel/sched_domain/cpuX/domainY/flags, I mean?
> Of course this will impact all tasks, not only KVM vcpus. But if the
> host does KVM only anyway...

Even a host dedicated to KVM has many non-KVM processes. I suspect an
increasing number of hosts will be split between VMs and containers.

> Regards

Christophe de Dinechin