Re: [PATCH 1/5] perf/x86/intel/uncore: Parse uncore discovery tables

[Liang, Kan]

On 3/16/2021 10:05 AM, Peter Zijlstra wrote:
> On Tue, Mar 16, 2021 at 08:42:25AM -0400, Liang, Kan wrote:
> > On 3/16/2021 7:43 AM, Peter Zijlstra wrote:
> > > On Fri, Mar 12, 2021 at 08:34:34AM -0800, kan.liang@xxxxxxxxxxxxxxx wrote:
> > > > From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> > > >
> > > > A self-describing mechanism for the uncore PerfMon hardware has been
> > > > introduced with the latest Intel platforms. By reading through an MMIO
> > > > page worth of information, perf can 'discover' all the standard uncore
> > > > PerfMon registers in a machine.
> > > >
> > > > The discovery mechanism relies on BIOS's support. With a proper BIOS,
> > > > a PCI device with the unique capability ID 0x23 can be found on each
> > > > die. Perf can retrieve the information of all available uncore PerfMons
> > > > from the device via MMIO. The information is composed of one global
> > > > discovery table and several unit discovery tables.
> > >
> > > > If a BIOS doesn't support the 'discovery' mechanism, there is nothing
> > > > changed.
> > >
> > > What if the BIOS got it wrong? Will the driver still get it correct if
> > > it is a known platform?
> >
> > Yes, I will submit a platform specific patch to fix this case.
> >
> > > Do we need a chicken flag to kill the discovery? uncore_no_discover?
> >
> > Yes, I plan to introduce a .use_discovery_tables flag to indicate whether to
> > use the discovery tables for the known platform.
> >
> > The below codes is part of the upcoming SPR uncore patches.
> > The first SPR uncore patch will still rely on the BIOS discovery tables,
> > because some uncore block information hasn't been published yet. We have to
> > retrieve the information fro the tables. Once all the information is
> > published, we can kill the discovery by removing the ".use_discovery_tables
> > = true".
>
> I was thinking of a module parameter, such that we can tell it to skip
> discovery on module load time etc.

Sure, I will add a module parameter, uncore_no_discover.
If users don't want the discovery feature, they can set 
uncore_no_discover=true.

Thanks,
Kan