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

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Date:   Tue, 16 Mar 2021 08:42:25 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, acme@...hat.com, linux-kernel@...r.kernel.org,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        eranian@...gle.com, namhyung@...nel.org, ak@...ux.intel.com
Subject: Re: [PATCH 1/5] perf/x86/intel/uncore: Parse uncore discovery tables



On 3/16/2021 7:43 AM, Peter Zijlstra wrote:
> On Fri, Mar 12, 2021 at 08:34:34AM -0800, kan.liang@...ux.intel.com wrote:
>> From: Kan Liang <kan.liang@...ux.intel.com>
>>
>> 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".

+static const struct intel_uncore_init_fun spr_uncore_init __initconst = {
+       .cpu_init = spr_uncore_cpu_init,
+       .pci_init = spr_uncore_pci_init,
+       .mmio_init = spr_uncore_mmio_init,
+       .use_discovery_tables = true,
+};

Thanks,
Kan