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?
... in the PERF_EV_CAP_READ_ACTIVE_PKG case, we can use the exiting(?)
package
masks, and more generally we can re-use the PMU's affinit mask if it
has one.
That said, I see that many pmu::read() implementations have
side-effects on
hwc->prev_count, and event->count, so I worry that this won't be sfe in
general
(e.g. if we race with the IRQ handler on another CPU).
Yeah, this doesn't have to be mandatory. It can be an optional mask the
PMU can set up during perf event init.
Peter,
Is this something that's acceptable to you?
Thanks,
Saravana
