From: Mark Rutland <mark.rutland@arm.com>
To: skannan@codeaurora.org
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
avilaj@codeaurora.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 2/2] perf/core: Add support for PMUs that can be read from any CPU
Date: Tue, 27 Feb 2018 11:43:14 +0000 [thread overview]
Message-ID: <20180227114313.mtvyo6rdavqfj2hy@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <90e7ff7d7dc1054db356fb1740ddb990@codeaurora.org>
On Mon, Feb 26, 2018 at 06:11:45PM -0800, skannan@codeaurora.org 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?
Thanks,
Mark.
next prev parent reply other threads:[~2018-02-27 11:43 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-24 0:19 [PATCH v1 1/2] perf/core: Add API to look up PMU type by name Saravana Kannan
2018-02-24 0:19 ` [PATCH v1 2/2] perf/core: Add support for PMUs that can be read from any CPU Saravana Kannan
2018-02-24 0:56 ` Saravana Kannan
2018-02-24 8:41 ` Peter Zijlstra
2018-02-27 1:53 ` skannan
2018-02-27 11:52 ` Mark Rutland
2018-03-03 15:41 ` Peter Zijlstra
2018-03-07 16:39 ` Jeremy Linton
2018-02-25 14:38 ` Mark Rutland
2018-02-27 2:11 ` skannan
2018-02-27 11:43 ` Mark Rutland [this message]
2018-02-27 23:15 ` skannan
2018-02-24 8:08 ` [PATCH v1 1/2] perf/core: Add API to look up PMU type by name Peter Zijlstra
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