linux-kernel - Re: [PATCH V2 4/6] x86/intel_rdt: Add helper to obtain performance counter index

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Date:   Thu, 6 Sep 2018 16:26:24 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     tglx@...utronix.de, fenghua.yu@...el.com, tony.luck@...el.com,
        mingo@...hat.com, acme@...nel.org, vikas.shivappa@...ux.intel.com,
        gavin.hindman@...el.com, jithu.joseph@...el.com,
        dave.hansen@...el.com, hpa@...or.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 4/6] x86/intel_rdt: Add helper to obtain performance
 counter index

Hi Peter,

On 9/6/2018 7:47 AM, Peter Zijlstra wrote:
> On Thu, Aug 16, 2018 at 01:16:07PM -0700, Reinette Chatre wrote:
> 
>> +static inline int x86_perf_rdpmc_ctr_get(struct perf_event *event)
>> +{
>> +	lockdep_assert_irqs_disabled();
>> +
>> +	return IS_ERR_OR_NULL(event) ? -1 : event->hw.event_base_rdpmc;
>> +}
> 
> That should be in arch/x86/include/asm/perf_event.h if anywhere. Also,
> call the thing x86_perf_rdpmc_index(), that's consistent with the other
> naming.

Moving it to arch/x86/include/asm/perf_event.h is not trivial since this
file is not familiar with struct perf_event.

struct perf_event, struct hw_perf_event and its member event_base_rdpmc
are all defined in include/linux/perf_event.h - could this function
perhaps be moved there? If so, would perf_rdpmc_index() perhaps be a
better name to be consistent with the other naming?

> 
> I don't think there's any point in testing for !event, this is an
> interface that mandates you know wth you're doing anyway.
> 

I could add:
/* !CONFIG_PERF_EVENTS */
static inline int perf_rdpmc_index(struct perf_event *event)
{
        return -1;
}

Reinette