linux-kernel - Re: [PATCH v6 3/4] bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter

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Message-ID: <20150805135932.GA18673@twins.programming.kicks-ass.net>
Date:	Wed, 5 Aug 2015 15:59:32 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Kaixu Xia <xiakaixu@...wei.com>
Cc:	ast@...mgrid.com, davem@...emloft.net, acme@...nel.org,
	mingo@...hat.com, masami.hiramatsu.pt@...achi.com,
	jolsa@...nel.org, daniel@...earbox.net, wangnan0@...wei.com,
	linux-kernel@...r.kernel.org, pi3orama@....com, hekuang@...wei.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH v6 3/4] bpf: Implement function bpf_perf_event_read()
 that get the selected hardware PMU conuter

On Wed, Aug 05, 2015 at 03:53:17PM +0200, Peter Zijlstra wrote:
> +/*
> + * NMI-safe method to read a local event, that is an event that
> + * is:
> + *   - either for the current task, or for this CPU
> + *   - does not have inherit set, for inherited task events
> + *     will not be local and we cannot read them atomically
> + *   - must not have a pmu::count method
> + */
> +u64 perf_event_read_local(struct perf_event *event)
> +{
> +	unsigned long flags;
> +	u64 val;
> +
> +	/*
> +	 * Disabling interrupts avoids all counter scheduling (context
> +	 * switches, timer based rotation and IPIs).
> +	 */
> +	local_irq_safe(flags);

Hmm, I think local_irq_save(flags) will compile much better. Obviously
this patch hasn't seen a compiler up close.
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