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: <55C23500.1000207@plumgrid.com>
Date:	Wed, 5 Aug 2015 09:08:32 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Kaixu Xia <xiakaixu@...wei.com>
Cc:	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 8/5/15 6:53 AM, Peter Zijlstra wrote:
> +	/*
> +	 * If the event is currently on this CPU, its either a per-task event,
> +	 * or local to this CPU. Furthermore it means its ACTIVE (otherwise
> +	 * oncpu == -1).
> +	 */
> +	if (event->oncpu == smp_processor_id())
> +		event->pmu->read(event);
> +
> +	val = local64_read(&event->count);
> +	local_irq_restore(flags);
> +

nice! cleaner and faster.
so raw_spin_lock(&ctx->lock) is not needed, because
update_*(event) methods are not called, right?

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