On 2018-02-27 03:43, Mark Rutland wrote:
On Mon, Feb 26, 2018 at 06:11:45PM -0800, [email protected] wrote:
On 2018-02-25 06:38, Mark Rutland wrote:
> On Fri, Feb 23, 2018 at 04:19:38PM -0800, Saravana Kannan wrote:
> > Some PMUs events can be read from any CPU. So allow the PMU to mark
> > events as such. For these events, we don't need to reject reads or
> > make smp calls to the event's CPU and cause unnecessary wake ups.
> >
> > Good examples of such events would be events from caches shared across
> > all CPUs.
>
> I think that if we need to generalize PERF_EV_CAP_READ_ACTIVE_PKG, it
> would be
> better to give events a pointer to a cpumask. That could then cover all
> cases
> quite trivially:
>
> static int __perf_event_read_cpu(struct perf_event *event, int
> event_cpu)
> {
> int local_cpu = smp_processor_id();
>
> if (event->read_mask &&
> cpumask_test_cpu(local_cpu, event->read_mask))
> event_cpu = local_cpu;
>
> return event_cpu;
> }
This is a good improvement on my attempt. If I send a patch for this,
is
that something you'd be willing to incorporate into your patch set and
make
sure the DSU pmu driver handles it correctly?
As I commented, I don't think that willl work without more invasive
changes as the DSU PMU's pmu::read() function has side effects on
hwc->prev_count and event_count, and could race with an IRQ handler on
another CPU.
Is the IPI really a problem in practice?
There are a bunch of cases, but the simplest one is if you try to
collect DSU stats (for analysis) while measuring power, it completely
messes up the power measurements.
Thanks,
Saravana
