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From: "Liang, Kan" <kan.liang@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@kernel.org, acme@redhat.com, linux-kernel@vger.kernel.org,
	alexander.shishkin@linux.intel.com, jolsa@redhat.com,
	eranian@google.com, namhyung@kernel.org, ak@linux.intel.com
Subject: Re: [PATCH 1/5] perf/x86/intel/uncore: Parse uncore discovery tables
Date: Tue, 16 Mar 2021 10:53:51 -0400	[thread overview]
Message-ID: <bdeda732-7b5e-1a99-29e4-e68d165822d1@linux.intel.com> (raw)
In-Reply-To: <YFC7GeBzL70QX2fS@hirez.programming.kicks-ass.net>



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@linux.intel.com wrote:
>>>> From: Kan Liang <kan.liang@linux.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".
> 
> 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

  reply	other threads:[~2021-03-16 14:54 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-12 16:34 [PATCH 0/5] Uncore PMON discovery mechanism support kan.liang
2021-03-12 16:34 ` [PATCH 1/5] perf/x86/intel/uncore: Parse uncore discovery tables kan.liang
2021-03-16 11:40   ` Peter Zijlstra
2021-03-16 12:29     ` Liang, Kan
2021-03-16 11:43   ` Peter Zijlstra
2021-03-16 12:42     ` Liang, Kan
2021-03-16 14:05       ` Peter Zijlstra
2021-03-16 14:53         ` Liang, Kan [this message]
2021-03-12 16:34 ` [PATCH 2/5] perf/x86/intel/uncore: Generic support for the MSR type of uncore blocks kan.liang
2021-03-12 16:34 ` [PATCH 3/5] perf/x86/intel/uncore: Rename uncore_notifier to uncore_pci_sub_notifier kan.liang
2021-03-12 16:34 ` [PATCH 4/5] perf/x86/intel/uncore: Generic support for the PCI type of uncore blocks kan.liang
2021-03-12 16:34 ` [PATCH 5/5] perf/x86/intel/uncore: Generic support for the MMIO " kan.liang

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