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SubjectRe: [PATCH 2/2] perf/x86/intel: Support PEBS output to PT
On Thu, May 02, 2019 at 01:50:22PM +0300, Alexander Shishkin wrote:
> If PEBS declares ability to output its data to Intel PT stream, use the
> aux_source attribute bit to enable PEBS data output to PT. This requires
> a PT event to be present and scheduled in the same context. Unlike the
> DS area, the kernel does not extract PEBS records from the PT stream to
> generate corresponding records in the perf stream, because that would
> require real time in-kernel PT decoding, which is not feasible. The PMI,
> however, can still be used.
>
> The output setting is per-CPU, so all PEBS events must be either writing
> to PT or to the DS area, so in order to not mess up the event scheduling,
> we fall back to the latter in case both types of events are scheduled in.
>
> Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> ---
> arch/x86/events/intel/core.c | 13 +++++++
> arch/x86/events/intel/ds.c | 59 +++++++++++++++++++++++++++++++-
> arch/x86/events/perf_event.h | 9 +++++
> arch/x86/include/asm/msr-index.h | 3 ++
> 4 files changed, 83 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 4b4dac089635..949a589fd9b1 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -3291,6 +3291,19 @@ static int intel_pmu_hw_config(struct perf_event *event)
> }
> }
>
> + if (event->attr.aux_source) {
> + if (!event->attr.precise_ip)
> + return -EINVAL;
> +
> + if (!x86_pmu.intel_cap.pebs_output_pt_available)
> + return -EOPNOTSUPP;
> +
> + event->hw.flags |= PERF_X86_EVENT_PEBS_VIA_PT;
> +
> + /* Signal to the core that we handled it */
> + event->attr.aux_source = 0;

That's a bit yuck, ideally we'd not modify attrs.

Can't we change that test in perf_event_alloc() to something like:

if (event->attr.aux_source &&
!(pmu->capabilities & PERF_PMU_CAP_AUX_SOURCE))
// error

?


> + }

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