linux-kernel - Re: [PATCH 7/18] 2.6.17.9 perfmon2 patch for review: PMU interruption support

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Message-Id: <20060823154057.4d6d444b.akpm@osdl.org>
Date:	Wed, 23 Aug 2006 15:40:57 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Stephane Eranian <eranian@...nkl.hpl.hp.com>
Cc:	linux-kernel@...r.kernel.org, eranian@....hp.com
Subject: Re: [PATCH 7/18] 2.6.17.9 perfmon2 patch for review: PMU
 interruption support

On Wed, 23 Aug 2006 01:05:58 -0700
Stephane Eranian <eranian@...nkl.hpl.hp.com> wrote:

> ...
>
> +irqreturn_t pfm_interrupt_handler(int irq, void *arg, struct pt_regs *regs)
> +{
> +	u64 start_cycles, total_cycles;
> +
> +	get_cpu();
> +
> +	start_cycles = pfm_arch_get_itc();
> +
> +	__pfm_interrupt_handler(regs);
> +
> +	total_cycles = pfm_arch_get_itc();
> +
> +	__get_cpu_var(pfm_stats).pfm_ovfl_intr_cycles += total_cycles - start_cycles;
> +
> +	put_cpu_no_resched();
> +	return IRQ_HANDLED;
> +}

If this code is only ever called from interrupt context then I suspect the
get_cpu() is not needed.  __get_cpu_var() requires that preemption be
disabled (so we cannot wander over to a different CPU midway) but IRQ
code doesn't get preempted.

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