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Subject: RE: [PATCH v3 0/4] add support for self monitoring
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From: =?iso-8859-1?Q?Morten_Br=F8rup?= <mb@smartsharesystems.com>
To: "Tomasz Duszynski" <tduszynski@marvell.com>,
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> From: Tomasz Duszynski [mailto:tduszynski@marvell.com]
> Sent: Tuesday, 29 November 2022 10.28
>=20
> This series adds self monitoring support i.e allows to configure and
> read performance measurement unit (PMU) counters in runtime without
> using perf utility. This has certain adventages when application runs
> on
> isolated cores with nohz_full kernel parameter.
>=20
> Events can be read directly using rte_pmu_read() or using dedicated
> tracepoint rte_eal_trace_pmu_read(). The latter will cause events to =
be
> stored inside CTF file.
>=20
> By design, all enabled events are grouped together and the same group
> is attached to lcores that use self monitoring funtionality.
>=20
> Events are enabled by names, which need to be read from standard
> location under sysfs i.e
>=20
> /sys/bus/event_source/devices/PMU/events
>=20
> where PMU is a core pmu i.e one measuring cpu events. As of today
> raw events are not supported.

Hi Thomasz,

I am very interested in this patch series for fast path profiling =
purposes. (Not using EAL trace, but our proprietary profiler.)

However, it seems that rte_pmu_read() is quite longwinded, compared to =
rte_pmu_pmc_read().

But perhaps I am just worrying too much, so I will ask: What is the =
performance cost of using rte_pmu_read() - compared to =
rte_pmu_pmc_read() - in the fast path?

If there is a non-negligible difference, could you please provide an =
example of how to configure PMU events and use rte_pmu_pmc_read() in an =
application?

I would primarily be interested in data cache misses and branch =
mispredictions. But feel free to make your own choices for the example.