Re: [PATCH 9/9] sched/psi: add PSI_IRQ to track IRQ/SOFTIRQ pressure

[Abel Wu]

On 7/22/22 2:13 PM, Chengming Zhou Wrote:
> On 2022/7/22 11:30, Abel Wu wrote:
> > Hi Chengming,
> >
> > On 7/21/22 12:04 PM, Chengming Zhou Wrote:
> > > Now PSI already tracked workload pressure stall information for
> > > CPU, memory and IO. Apart from these, IRQ/SOFTIRQ could have
> > > obvious impact on some workload productivity, such as web service
> > > workload.
> > >
> > > When CONFIG_IRQ_TIME_ACCOUNTING, we can get IRQ/SOFTIRQ delta time
> > > from update_rq_clock_task(), in which we can record that delta
> > > to CPU curr task's cgroups as PSI_IRQ_FULL status.
> >
> > The {soft,}irq affection should be equal to all the runnable tasks
> > on that cpu, not only rq->curr. Further I think irqstall is per-cpu
> > rather than per-cgroup.
>
> Although IRQ/SOFTIRQ is per-cpu, it's the rq->curr who own the CPU at the time
> and pay for it, meanwhile other groups would be thought as PSI_CPU_FULL.

I don't think rq->curr pays for it if you mean consuming quota here.
And it doesn't seem appropriate to let other groups treat it as cpu
stall because the rq->curr is also the victim rather than the one
causes stall (so it's different from rq->curr causing memstall and
observed as cpustall by others).

> So I think it's reasonable to account this IRQ/SOFTIRQ delta to rq->curr's groups
> as PSI_IRQ_FULL pressure stall. And per-cpu IRQ stall can also get from psi_system.