Re: [RFC][PATCH 10/10] sched/eevdf: Use sched_attr::sched_runtime to set request/slice suggestion

[Chen Yu]

On 2024-04-05 at 12:28:04 +0200, Peter Zijlstra wrote:
> Allow applications to directly set a suggested request/slice length using
> sched_attr::sched_runtime.
> 
> The implementation clamps the value to: 0.1[ms] <= slice <= 100[ms]
> which is 1/10 the size of HZ=1000 and 10 times the size of HZ=100.
> 
> Applications should strive to use their periodic runtime at a high
> confidence interval (95%+) as the target slice. Using a smaller slice
> will introduce undue preemptions, while using a larger value will
> increase latency.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
>

Is it possible to leverage this task slice to do better task wakeup placement?
The idea is that, the smaller the slice the wakee has, the less idle CPU it
should scan. This can reduce wake latency and inhibit costly task migration,
especially on large systems.

We did some experiments and got some performance improvements: