Re: [PATCH v2 2/2] credit: Don't steal vcpus which have yielded

[Marcus Granado <marcus.granado@xxxxxxxxx>]

On Thu, 21 Sept 2023 at 15:14, George Dunlap <george.dunlap@xxxxxxxxx> wrote:
>
> On Thu, Sep 21, 2023 at 1:23 PM George Dunlap <george.dunlap@xxxxxxxxx> wrote:
> >
> > On large systems with many vcpus yielding due to spinlock priority
> > inversion, it's not uncommon for a vcpu to yield its timeslice, only
> > to be immediately stolen by another pcpu looking for higher-priority
> > work.
> >
> > To prevent this:
> >
> > * Keep the YIELD flag until a vcpu is removed from a runqueue
> >
> > * When looking for work to steal, skip vcpus which have yielded
> >
>
> Marcus,
>
> Just wanted to verify my interpretation of the testing you did of this
> patch several months ago:
>
> 1. On the problematic workload, mean execution time for the task under
> heavy load was around 12 seconds
> 2. With only patch 2 of this series (0004 in your tests), mean
> execution time under heavy load was around 5 seconds
> 3. With only patch 1 of this series (0003 in your tests), mean
> execution time under heavy load was around 3 seconds
> 4. With both patch 1 and patch 2 of this series (0003+0004 in your
> tests), mean execution time under heavy load was also around 3 seconds
>
> So both patches independently exhibit an improvement; but the combined
> effect is about the same as the first patch.
>
Yes, thanks for the summary, that's pretty much it.
Marcus