linux-kernel - Re: [PATCH V2 20/30] coresight: etb10: implementing buffer set/reset() API

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Date:	Tue, 20 Oct 2015 12:56:47 +0300
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Mathieu Poirier <mathieu.poirier@...aro.org>,
	gregkh@...uxfoundation.org, a.p.zijlstra@...llo.nl,
	acme@...nel.org, mingo@...hat.com, corbet@....net,
	nicolas.pitre@...aro.org
Cc:	adrian.hunter@...el.com, zhang.chunyan@...aro.org,
	mike.leach@....com, tor@...com, al.grant@....com,
	pawel.moll@....com, linux-arm-kernel@...ts.infradead.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	mathieu.poirier@...aro.org
Subject: Re: [PATCH V2 20/30] coresight: etb10: implementing buffer set/reset() API

Mathieu Poirier <mathieu.poirier@...aro.org> writes:

> Implementing perf related APIs to activate and terminate
> a trace session.  More specifically dealing with the sink
> buffer's internal mechanic along with perf's API to start
> and stop interactions with the ring buffers.

A matter of preference, but I'd say that it would be easier to review
this part if you merged all the buffer related patches together.

> +static void etb_reset_buffer(struct coresight_device *csdev,
> +			     struct perf_output_handle *handle,
> +			     void *sink_config)
> +{
> +	struct cs_buffers *buf = sink_config;
> +	struct etb_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> +
> +	if (buf) {
> +		/*
> +		 * In snapshot mode ->data_size holds the new address of the
> +		 * ring buffer's head.  The size itself is the whole address
> +		 * range since we want the latest information.
> +		 */
> +		if (buf->snapshot)
> +			handle->head = local_xchg(&buf->data_size,
> +						  buf->nr_pages << PAGE_SHIFT);

Does it make sense to do this in etb_update_buffer() instead?

> +		perf_aux_output_end(handle, local_xchg(&buf->data_size, 0),
> +				    local_xchg(&buf->lost, 0));

The corresponding perf_aux_output_begin() is done in etm_event_add(),
I'd suggest that you do this in etm_event_del(),
unconditionally. Otherwise you're risking ending up with a refcount leak
and all sorts of horror.

Regards,
--
Alex
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