Re: [PATCH] perf/core: move all of the pmu devices into their own location

Greg Kroah-Hartman
2025-02-04T18:03:33Z

On Tue, Feb 04, 2025 at 09:49:55AM -0800, Ian Rogers wrote:
> On Tue, Feb 4, 2025 at 9:12 AM Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
> >
> > On Tue, Feb 04, 2025 at 11:41:38AM -0500, Vince Weaver wrote:
> > > On Tue, 4 Feb 2025, Greg Kroah-Hartman wrote:
> > >
> > > >
> > > > It seems that the majority of the perf code IS looking in the correct
> > > > place, just mem-events.c seemed wrong.
> > >
> > > I hate to tell you, but other places in userspace are depending on the
> > > current setup. libpfm4, used by PAPI, is looking directly in /sys/devices
> > > for pmus and will break with the changes you are planning.
> >
> > Then that too needs to be fixed, sorry. Again, devices can, and will,
> > move around in /sys/devices/ you can never hard-code any paths there.
> > Any userspace code must ALWAYS be able to handle that, that's a sysfs
> > requirement.
> >
> > And do you have a link to the source for that code? Good news is that
> > if the code is fixed in userspace, it will work for any kernel (old or
> > new).
>
> +Stephane Eranian
>
> I see use of /sys/devices in at least:
> https://sourceforge.net/p/perfmon2/libpfm4/ci/master/tree/lib/pfmlib_perf_event_pmu.c
> I imagine it isn't a big job to clean it up.

Nope, all that has to happen is this line:
snprintf(buf, PATH_MAX, "/sys/devices/%s/events/%s", e->pmu ? e->pmu : "cpu", e->name);
be changed to:
snprintf(buf, PATH_MAX, "/sys/bus/event_source/devices/%s/events/%s", e->pmu ? e->pmu : "cpu", e->name);

thanks,

greg k-h