linux-kernel - Re: [PATCH 2/7] ARM: perf_event: Support percpu irqs for the CPU PMU

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Message-ID: <20140110193657.GG14405@codeaurora.org>
Date:	Fri, 10 Jan 2014 11:36:57 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Will Deacon <will.deacon@....com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/7] ARM: perf_event: Support percpu irqs for the CPU
 PMU

On 01/10, Will Deacon wrote:
> On Thu, Jan 09, 2014 at 07:17:29PM +0000, Stephen Boyd wrote:
> 
> > We can avoid the hacky cast of the per-cpu dev token by using the
> > cpu_pmu pointer directly, but we'll still need to pass something to the
> > percpu interrupt handler otherwise the genirq layer doesn't allow us to
> > request the PPI. I can pass hw_events I guess. Is that what you're
> > thinking? Or were you thinking that we could just use
> > cpu_pmu->handle_irq as the handler argument in request_percpu_irq()? I
> > can't figure out how that is supposed to work.
> 
> Actually, I was thinking you could remove cpu_pmu_dispatch_irq completely
> and just pass the actual handler straight through to request_percpu_irq. On
> arm64 we pass the hw_events as the pcpu token, so I'd be inclined to do the
> same here unless there's a good reason not to.
> 

Passing the hw_events as the pcpu token here is kind of hacky.
The reason is because the token is dereferenced into cpu_pmu in
armv7pmu_handle_irq() like so:

	struct arm_pmu *cpu_pmu = (struct arm_pmu *)dev;

It would be great if we could pass cpu_pmu directly to the
request call like so:

	request_percpu_irq(irq, cpu_pmu->handle_irq, "arm-pmu", &cpu_pmu);

but no. request_percpu_irq() wants a percpu pointer so this won't
work. If cpu_pmu was declared as DEFINE_PER_CPU, this would work
out just fine.

Should the cpu_pmu become a per-cpu variable? That sounds rather
invasive.

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