linux-kernel - Re: [patch/rfc] perf on raspberry-pi without overflow interrupt

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Message-ID: <20140110100804.GB11045@mudshark.cambridge.arm.com>
Date:	Fri, 10 Jan 2014 10:08:04 +0000
From:	Will Deacon <will.deacon@....com>
To:	Vince Weaver <vincent.weaver@...ne.edu>
Cc:	Chad Paradis <chad.paradis@...t.maine.edu>,
	Peter Zijlstra <peterz@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Stephane Eranian <eranian@...il.com>
Subject: Re: [patch/rfc] perf on raspberry-pi without overflow interrupt

On Fri, Jan 10, 2014 at 04:08:47AM +0000, Vince Weaver wrote:
> On Thu, 9 Jan 2014, Will Deacon wrote:
> 
> > I'd rather see it in the generic code if at all possible. Maybe we could add
> > a flags field to perf_pmu_register?
> 
> I can look into adding the check in generic code.
> 
> In the meantime, would you consider a patch like this that disables
> the IRQ check and lets ARM devices missing an IRQ (such as the rasp-pi)
> still have access to the counters?

In the absence of a core change, I think I'd rather have something like your
second patch, but without the extra no_overflow_irq field (you can check the
platform device, as I mentioned previously).

Cheers,

Will

> 
> diff --git a/arch/arm/kernel/perf_event_cpu.c b/arch/arm/kernel/perf_event_cpu.c
> index d85055c..ff1a752 100644
> --- a/arch/arm/kernel/perf_event_cpu.c
> +++ b/arch/arm/kernel/perf_event_cpu.c
> @@ -97,8 +97,8 @@ static int cpu_pmu_request_irq(struct arm_pmu *cpu_pmu, irq_handler_t handler)
>  
>  	irqs = min(pmu_device->num_resources, num_possible_cpus());
>  	if (irqs < 1) {
> -		pr_err("no irqs for PMUs defined\n");
> -		return -ENODEV;
> +		printk_once("no irqs for PMUs defined, sampling events not supported\n");
> +		return 0;
>  	}
>  
>  	for (i = 0; i < irqs; ++i) {
> 
> 
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