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

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Date:	Thu, 9 Jan 2014 23:08:47 -0500 (EST)
From:	Vince Weaver <vincent.weaver@...ne.edu>
To:	Will Deacon <will.deacon@....com>
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 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?


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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