Re: [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED

Steven Rostedt
2023-10-26T12:48:20Z

On Thu, 26 Oct 2023 16:50:16 +0900
Sergey Senozhatsky <senozhatsky@chromium.org> wrote:

> > The goal is to prevent a thread / vCPU being preempted while holding a lock
> > or resource that other threads / vCPUs will want. That is, prevent
> > contention, as that's usually the biggest issue with performance in user
> > space and VMs.
>
> I think some time ago we tried to check guest's preempt count on each vm-exit
> and we'd vm-enter if guest exited from a critical section (those that bump
> preempt count) so that it can hopefully finish whatever is was going to
> do and vmexit again. We didn't look into covering guest's RCU read-side
> critical sections.
>
> Can you educate me, is your PoC significantly different from guest preempt
> count check?

No, it's probably very similar. Just the mechanism to allow it to run
longer may be different.

-- Steve