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Subject: Re: [PATCH v2 26/27] coresight: perf: Remove reset_buffer call back
 for sinks
To:     Mathieu Poirier <mathieu.poirier@linaro.org>
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        mike.leach@linaro.org, robert.walker@arm.com, mark.rutland@arm.com,
        will.deacon@arm.com, robin.murphy@arm.com, sudeep.holla@arm.com,
        frowand.list@gmail.com, robh@kernel.org, john.horley@arm.com
References: <1525165857-11096-1-git-send-email-suzuki.poulose@arm.com>
 <1525165857-11096-27-git-send-email-suzuki.poulose@arm.com>
 <20180508194241.GC3389@xps15>
From:   Suzuki K Poulose <Suzuki.Poulose@arm.com>
Message-ID: <7478286d-cbbe-4bf2-4012-f4469133f4b2@arm.com>
Date:   Fri, 11 May 2018 17:35:19 +0100
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On 08/05/18 20:42, Mathieu Poirier wrote:
> On Tue, May 01, 2018 at 10:10:56AM +0100, Suzuki K Poulose wrote:
>> Right now we issue an update_buffer() and reset_buffer() call backs
>> in succession when we stop tracing an event. The update_buffer is
>> supposed to check the status of the buffer and make sure the ring buffer
>> is updated with the trace data. And we store information about the
>> size of the data collected only to be consumed by the reset_buffer
>> callback which always follows the update_buffer. This was originally
>> designed for handling future IPs which could trigger a buffer overflow
>> interrupt. This patch gets rid of the reset_buffer callback altogether
>> and performs the actions in update_buffer, making it return the size
>> collected. We can always add the support for handling the overflow
>> interrupt case later.
>>
>> This removes some not-so pretty hack (storing the new head in the
>> size field for snapshot mode) and cleans it up a little bit.
> 
> IPs with an overflow interrupts will be arriving shortly, so it is not like the
> future is uncertain - they are coming.  Right now the logic is there - I don't
> see a real need to consolidate things only to split it again in the near future.
> 
> I agree the part about overloading buf->data_size with the head of the ring
> buffer when operating in snapshot mode isn't pretty (though well documented).
> If anything that can be improve, i.e add a buf->head and things will be clear.
> Once again this could be part of another patchset.
> 

Mathieu,

I am not sure how was this supposed to be used in conjunction with the overflow
handling. Please could you help me here ? I might be able to retain
the callback and possibly improve it with the changes for etr_buf infrastructure.

Cheers
Suzuki


>>
>> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>> ---
>>   drivers/hwtracing/coresight/coresight-etb10.c    | 56 +++++------------------
>>   drivers/hwtracing/coresight/coresight-etm-perf.c |  9 +---
>>   drivers/hwtracing/coresight/coresight-tmc-etf.c  | 58 +++++-------------------
>>   include/linux/coresight.h                        |  5 +-
>>   4 files changed, 26 insertions(+), 102 deletions(-)
>>
>> diff --git a/drivers/hwtracing/coresight/coresight-etb10.c b/drivers/hwtracing/coresight/coresight-etb10.c
>> index d9c2f87..b13712a 100644
>> --- a/drivers/hwtracing/coresight/coresight-etb10.c
>> +++ b/drivers/hwtracing/coresight/coresight-etb10.c
>> @@ -322,37 +322,7 @@ static int etb_set_buffer(struct coresight_device *csdev,
>>   	return ret;
>>   }
>>   
>> -static unsigned long etb_reset_buffer(struct coresight_device *csdev,
>> -				      struct perf_output_handle *handle,
>> -				      void *sink_config)
>> -{
>> -	unsigned long size = 0;
>> -	struct cs_buffers *buf = sink_config;
>> -
>> -	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);
>> -
>> -		/*
>> -		 * Tell the tracer PMU how much we got in this run and if
>> -		 * something went wrong along the way.  Nobody else can use
>> -		 * this cs_buffers instance until we are done.  As such
>> -		 * resetting parameters here and squaring off with the ring
>> -		 * buffer API in the tracer PMU is fine.
>> -		 */
>> -		size = local_xchg(&buf->data_size, 0);
>> -	}
>> -
>> -	return size;
>> -}
>> -
>> -static void etb_update_buffer(struct coresight_device *csdev,
>> +static unsigned long etb_update_buffer(struct coresight_device *csdev,
>>   			      struct perf_output_handle *handle,
>>   			      void *sink_config)
>>   {
>> @@ -361,13 +331,13 @@ static void etb_update_buffer(struct coresight_device *csdev,
>>   	u8 *buf_ptr;
>>   	const u32 *barrier;
>>   	u32 read_ptr, write_ptr, capacity;
>> -	u32 status, read_data, to_read;
>> -	unsigned long offset;
>> +	u32 status, read_data;
>> +	unsigned long offset, to_read;
>>   	struct cs_buffers *buf = sink_config;
>>   	struct etb_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>>   
>>   	if (!buf)
>> -		return;
>> +		return 0;
>>   
>>   	capacity = drvdata->buffer_depth * ETB_FRAME_SIZE_WORDS;
>>   
>> @@ -472,18 +442,17 @@ static void etb_update_buffer(struct coresight_device *csdev,
>>   	writel_relaxed(0x0, drvdata->base + ETB_RAM_WRITE_POINTER);
>>   
>>   	/*
>> -	 * In snapshot mode all we have to do is communicate to
>> -	 * perf_aux_output_end() the address of the current head.  In full
>> -	 * trace mode the same function expects a size to move rb->aux_head
>> -	 * forward.
>> +	 * In snapshot mode we have to update the handle->head to point
>> +	 * to the new location.
>>   	 */
>> -	if (buf->snapshot)
>> -		local_set(&buf->data_size, (cur * PAGE_SIZE) + offset);
>> -	else
>> -		local_add(to_read, &buf->data_size);
>> -
>> +	if (buf->snapshot) {
>> +		handle->head = (cur * PAGE_SIZE) + offset;
>> +		to_read = buf->nr_pages << PAGE_SHIFT;
>> +	}
>>   	etb_enable_hw(drvdata);
>>   	CS_LOCK(drvdata->base);
>> +
>> +	return to_read;
>>   }
>>   
>>   static const struct coresight_ops_sink etb_sink_ops = {
>> @@ -492,7 +461,6 @@ static const struct coresight_ops_sink etb_sink_ops = {
>>   	.alloc_buffer	= etb_alloc_buffer,
>>   	.free_buffer	= etb_free_buffer,
>>   	.set_buffer	= etb_set_buffer,
>> -	.reset_buffer	= etb_reset_buffer,
>>   	.update_buffer	= etb_update_buffer,
>>   };
>>   
>> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
>> index 4e5ed65..5096def 100644
>> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
>> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
>> @@ -342,15 +342,8 @@ static void etm_event_stop(struct perf_event *event, int mode)
>>   		if (!sink_ops(sink)->update_buffer)
>>   			return;
>>   
>> -		sink_ops(sink)->update_buffer(sink, handle,
>> +		size = sink_ops(sink)->update_buffer(sink, handle,
>>   					      event_data->snk_config);
>> -
>> -		if (!sink_ops(sink)->reset_buffer)
>> -			return;
>> -
>> -		size = sink_ops(sink)->reset_buffer(sink, handle,
>> -						    event_data->snk_config);
>> -
>>   		perf_aux_output_end(handle, size);
>>   	}
>>   
>> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c
>> index 0a32734..75ef5c4 100644
>> --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
>> +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
>> @@ -360,36 +360,7 @@ static int tmc_set_etf_buffer(struct coresight_device *csdev,
>>   	return ret;
>>   }
>>   
>> -static unsigned long tmc_reset_etf_buffer(struct coresight_device *csdev,
>> -					  struct perf_output_handle *handle,
>> -					  void *sink_config)
>> -{
>> -	long size = 0;
>> -	struct cs_buffers *buf = sink_config;
>> -
>> -	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);
>> -		/*
>> -		 * Tell the tracer PMU how much we got in this run and if
>> -		 * something went wrong along the way.  Nobody else can use
>> -		 * this cs_buffers instance until we are done.  As such
>> -		 * resetting parameters here and squaring off with the ring
>> -		 * buffer API in the tracer PMU is fine.
>> -		 */
>> -		size = local_xchg(&buf->data_size, 0);
>> -	}
>> -
>> -	return size;
>> -}
>> -
>> -static void tmc_update_etf_buffer(struct coresight_device *csdev,
>> +static unsigned long tmc_update_etf_buffer(struct coresight_device *csdev,
>>   				  struct perf_output_handle *handle,
>>   				  void *sink_config)
>>   {
>> @@ -398,17 +369,17 @@ static void tmc_update_etf_buffer(struct coresight_device *csdev,
>>   	const u32 *barrier;
>>   	u32 *buf_ptr;
>>   	u64 read_ptr, write_ptr;
>> -	u32 status, to_read;
>> -	unsigned long offset;
>> +	u32 status;
>> +	unsigned long offset, to_read;
>>   	struct cs_buffers *buf = sink_config;
>>   	struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>>   
>>   	if (!buf)
>> -		return;
>> +		return 0;
>>   
>>   	/* This shouldn't happen */
>>   	if (WARN_ON_ONCE(drvdata->mode != CS_MODE_PERF))
>> -		return;
>> +		return 0;
>>   
>>   	CS_UNLOCK(drvdata->base);
>>   
>> @@ -497,18 +468,14 @@ static void tmc_update_etf_buffer(struct coresight_device *csdev,
>>   		}
>>   	}
>>   
>> -	/*
>> -	 * In snapshot mode all we have to do is communicate to
>> -	 * perf_aux_output_end() the address of the current head.  In full
>> -	 * trace mode the same function expects a size to move rb->aux_head
>> -	 * forward.
>> -	 */
>> -	if (buf->snapshot)
>> -		local_set(&buf->data_size, (cur * PAGE_SIZE) + offset);
>> -	else
>> -		local_add(to_read, &buf->data_size);
>> -
>> +	/* In snapshot mode we have to update the head */
>> +	if (buf->snapshot) {
>> +		handle->head = (cur * PAGE_SIZE) + offset;
>> +		to_read = buf->nr_pages << PAGE_SHIFT;
>> +	}
>>   	CS_LOCK(drvdata->base);
>> +
>> +	return to_read;
>>   }
>>   
>>   static const struct coresight_ops_sink tmc_etf_sink_ops = {
>> @@ -517,7 +484,6 @@ static const struct coresight_ops_sink tmc_etf_sink_ops = {
>>   	.alloc_buffer	= tmc_alloc_etf_buffer,
>>   	.free_buffer	= tmc_free_etf_buffer,
>>   	.set_buffer	= tmc_set_etf_buffer,
>> -	.reset_buffer	= tmc_reset_etf_buffer,
>>   	.update_buffer	= tmc_update_etf_buffer,
>>   };
>>   
>> diff --git a/include/linux/coresight.h b/include/linux/coresight.h
>> index c0e1568..41b3729 100644
>> --- a/include/linux/coresight.h
>> +++ b/include/linux/coresight.h
>> @@ -212,10 +212,7 @@ struct coresight_ops_sink {
>>   	int (*set_buffer)(struct coresight_device *csdev,
>>   			  struct perf_output_handle *handle,
>>   			  void *sink_config);
>> -	unsigned long (*reset_buffer)(struct coresight_device *csdev,
>> -				      struct perf_output_handle *handle,
>> -				      void *sink_config);
>> -	void (*update_buffer)(struct coresight_device *csdev,
>> +	unsigned long (*update_buffer)(struct coresight_device *csdev,
>>   			      struct perf_output_handle *handle,
>>   			      void *sink_config);
>>   };
>> -- 
>> 2.7.4
>>