linux-kernel - Re: [RFC v2 6/7] perf: add api for pmus to write to AUX space

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Message-ID: <87fvitxmd8.fsf@ashishki-desk.ger.corp.intel.com>
Date:	Wed, 25 Jun 2014 14:24:51 +0300
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Robert Richter <rric@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [RFC v2 6/7] perf: add api for pmus to write to AUX space

Peter Zijlstra <peterz@...radead.org> writes:

> On Wed, Jun 11, 2014 at 06:41:49PM +0300, Alexander Shishkin wrote:
>> +void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size,
>> +			 bool truncated)
>> +{
>> +	struct ring_buffer *rb = handle->rb;
>> +	unsigned long aux_head;
>> +
>> +	aux_head = local_read(&rb->aux_head);
>> +	local_add(size, &rb->aux_head);
>> +
>> +	rb->user_page->aux_head = local_read(&rb->aux_head);
>> +	smp_wmb();
>> +
>> +	perf_output_wakeup(handle);
>> +	handle->event = NULL;
>> +
>> +	ring_buffer_put(rb);
>> +}
>
> This thing is distinctly less complex than perf_output_put_handle().. ?

This one doesn't support nested writers, but there shouldn't be any
either. But I notice now that the barrier is misplaced. Wakeup watermark
is not yet taken care of, but will be. Anything else I'm missing?

Regards,
--
Alex
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