RE: [PATCH v2] Added perf functionality to mmdc driver

[Zhengyu Shen]

> > 	Added cpumask and migration handling support to driver
> > 	Validated event during event_init
> > 	Added code to properly stop counters
> > 	Used perf_invalid_context instead of perf_sw_context
> > 	Added hrtimer to poll for overflow
> > 	Added better description
> > 	Added support for multiple mmdcs
> 
> As I commented on v1 w.r.t. the above, I would appreciate being Cc'd on
> future versions of this patch.

Sorry about that, I'll be sure to CC you in the future. 

> > +static void mmdc_event_start(struct perf_event *event, int flags) {
> > +	struct mmdc_pmu *pmu_mmdc = to_mmdc_pmu(event->pmu);
> > +	void __iomem *mmdc_base, *reg;
> > +
> > +	local64_set(&event->count, 0);
> > +	mmdc_base = pmu_mmdc->mmdc_base;
> > +	reg = mmdc_base + MMDC_MADPCR0;
> > +	hrtimer_start(&pmu_mmdc->hrtimer, mmdc_timer_period(),
> > +			HRTIMER_MODE_REL_PINNED);
> 
> Why is a hrtimer necessary? Is this just copy-pasted from CCN, or do you
> have similar HW issues?
> 
> Is there no overflow interrupt?

When overflow occurs, a register bit is set to one. There is no overflow
interrupt which is why the timer is needed. 

Thanks a lot for the feedback!