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

From: Alexei Starovoitov <[email-masked]>
Date: Wed, 5 Aug 2015 09:08:32 -0700

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?