Re: [PATCH v3 00/10] sched/fair, KVM: Semantics-aware directed yield for oversubscribed KVM

[Shrikanth Hegde]

Hi Wanpeng.

On 6/12/26 7:03 AM, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
>
> On overcommitted hosts, a spinning vCPU often calls yield_to() to let a
> lock holder or IPI receiver run.  The hint can be ineffective for two
> independent reasons: the scheduler may fail to select the nominated task,
> and KVM may nominate a task that is not the one the spinning vCPU is
> waiting for.

I was curious to try this as we have been working on paravirt scheduling
which aims at reducing the vCPU preemption based on the steal time.
https://lore.kernel.org/all/20260514152204.481115-1-sshegde@xxxxxxxxxxxxx/

I gave the patch series a try. With both real life workload(daytrader) and
micro-benchmarks (hackbench) I don't see any benefit. Note that it is running
the same workloads in all VM's at the same time.


I had thought about this series:
- Do you observe steal time when you run your workload? If yes, if you reduce the
  vCPU, IPI will natually move to reduced set and due to reduction in vCPU preemption
  yeild also may not be necessary.

- is there vCPU pinning? workload is pinned separately to explicit vCPUs.

- Is only a few vCPUs doing the locks in the workload you have mentioned in the
  cover-letter?