linux-kernel - Re: [PATCH 10/11] x86: perf_event_intel_bts.c: use arch

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Date:	Mon, 1 Jun 2015 11:35:18 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	<linux-kernel@...r.kernel.org>, Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, <x86@...nel.org>
Subject: Re: [PATCH 10/11] x86: perf_event_intel_bts.c: use arch_initcall
 to hook in enabling

On 15-06-01 10:14 AM, Peter Zijlstra wrote:
> On Mon, 2015-06-01 at 10:11 -0400, Paul Gortmaker wrote:
>> On 15-06-01 03:04 AM, Peter Zijlstra wrote:
>>> On Sun, May 31, 2015 at 08:54:11PM -0400, Paul Gortmaker wrote:
>>>> This was using module_init, but there is no way this code can
>>>> be modular.  
>>>
>>> No, I think you could actually make it modular if you really wanted to.
>>
>> By "really wanted to" -- do you mean future changes that someone might do?
> 
> Yeah, I think we read "no way this code can be modular" differently.
> 
> I'm reading it like; it can easily be, all it requires is this little
> patch, where you're reading it like Kconfig changes.

OK, so how about I update both logs with something like this, to
clarify I meant "no way this code can be modular currently, given
the existing Kconfig situation":

----------------------8<---------------------------

This was using module_init, but the current Kconfig situation is
as follows:

In arch/x86/kernel/cpu/Makefile:

  obj-$(CONFIG_CPU_SUP_INTEL)    += perf_event_intel_pt.o perf_event_intel_bts.o

and in arch/x86/Kconfig.cpu:

  config CPU_SUP_INTEL
        default y
        bool "Support Intel processors" if PROCESSOR_SELECT

So currently, the end user can not build this code into a module.
If in the future, there is desire for this to be modular, then
it can be changed to include <linux/module.h> and use module_init.

But currently, in the non-modular case, a module_init becomes a
device_initcall.  But this really isn't a device, so we should
choose a more appropriate initcall bucket to put it in.

The obvious choice here seems to be arch_initcall, but that does
make it earlier than it was currently through device_initcall.
As long as perf_pmu_register() is functional, we should be OK.

 
----------------------8<----------------------------------

Paul.

> 
> 
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