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Subject: RE: [PATCH 6/6] trace: add PMU
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Date: Mon, 16 Jun 2025 15:18:02 +0200
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Thread-Topic: [PATCH 6/6] trace: add PMU
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References: <21436140.jiFIW2sfyF@thomas>
 <20250616094903.3236231-1-tduszynski@marvell.com>
From: =?iso-8859-1?Q?Morten_Br=F8rup?= <mb@smartsharesystems.com>
To: "Tomasz Duszynski" <tduszynski@marvell.com>,
	<thomas@monjalon.net>
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> From: Tomasz Duszynski [mailto:tduszynski@marvell.com]
> Sent: Monday, 16 June 2025 11.49
>=20
> >16/06/2025 08:53, Tomasz Duszynski:
> >> @@ -86,6 +86,7 @@ always_enable =3D [
> >>          'ring',
> >>          'stack',
> >>          'telemetry',
> >> +        'pmu',
> >>  ]
> >
> >This list is alphabetically sorted.
>=20
> Right, missed that.
>=20
> >
> >What is the justification for always enabling PMU lib?
> >Is it a good idea to always enable an experimental library?
>=20
> Well, since on Linux eal depends on pmu, disabling pmu ends up =
disabling
> eal, which breaks minimal build.
>=20
> As for the second question - no. I think ideally lib should remain
> optional. However, since trace is part of eal, that indirectly forces
> pmu to be built.

Trace is optional, controlled by RTE_TRACE in /config/rte_config.h.

>=20
> Alternatively, I guess we could make the library explicitly optional =
by
> extra meson option. But given that there are already options for
> controlling libraries that approach is not perfect either.

PMU should depend on EAL, not the other way around.

Please refer to this fix, where pmu.c is updated to call =
rte_mem_page_size(), which includes error handling, instead of directly =
calling sysconf(_SC_PAGE_SIZE) without handling errors from it:
https://patchwork.dpdk.org/project/dpdk/patch/20250612140657.313785-1-mb@=
smartsharesystems.com/

If there are cross dependency issues due to integration between PMU and =
Trace, adding the PMU related trace directly in the Trace library is a =
much better solution than making EAL depend on PMU.

Also, I agree with Thomas that PMU should not be considered a mandatory =
core library (always_enable).