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

Thomas Gleixner
2023-09-19T09:20:18Z

On Mon, Sep 18 2023 at 20:21, Andy Lutomirski wrote:
> On Wed, Aug 30, 2023, at 11:49 AM, Ankur Arora wrote:

> Why do we support anything other than full preempt? I can think of
> two reasons, neither of which I think is very good:
>
> 1. Once upon a time, tracking preempt state was expensive. But we fixed that.
>
> 2. Folklore suggests that there's a latency vs throughput tradeoff,
> and serious workloads, for some definition of serious, want
> throughput, so they should run without full preemption.

It's absolutely not folklore. Run to completion is has well known
benefits as it avoids contention and avoids the overhead of scheduling
for a large amount of scenarios.

We've seen that painfully in PREEMPT_RT before we came up with the
concept of lazy preemption for throughput oriented tasks.

Thanks,

tglx