linux-kernel - Re: [PATCH v2 05/10] coresight: trbe: Drop duplicate TRUNCATE flags

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Date:   Fri, 30 Jul 2021 13:58:48 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        coresight@...ts.linaro.org
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        tamas.zsoldos@....com, al.grant@....com, leo.yan@...aro.org,
        mike.leach@...aro.org, mathieu.poirier@...aro.org,
        jinlmao@....qualcomm.com
Subject: Re: [PATCH v2 05/10] coresight: trbe: Drop duplicate TRUNCATE flags

On 30/07/2021 05:47, Anshuman Khandual wrote:
> 
> 
> On 7/23/21 6:16 PM, Suzuki K Poulose wrote:
>> We mark the buffer as TRUNCATED when there is no space left
>> in the buffer. But we do it at different points.
>>      __trbe_normal_offset()
>> and also, at all the callers of the above function via
>> compute_trbe_buffer_limit(), when the limit == base (i.e
>> offset = 0 as returned by the __trbe_normal_offset()).
>>
>> So, given that the callers already mark the buffer as TRUNCATED
>> drop the caller inside the __trbe_normal_offset().
>>
>> This is in preparation to moving the handling of TRUNCATED
>> into a central place.
>>
>> Cc: Anshuman Khandual <anshuman.khandual@....com>
>> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
>> Cc: Mike Leach <mike.leach@...aro.org>
>> Cc: Leo Yan <leo.yan@...aro.org>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>> ---
>>   drivers/hwtracing/coresight/coresight-trbe.c | 7 +------
>>   1 file changed, 1 insertion(+), 6 deletions(-)
>>
>> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
>> index 446f080f8320..62e1a08f73ff 100644
>> --- a/drivers/hwtracing/coresight/coresight-trbe.c
>> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
>> @@ -253,13 +253,9 @@ static unsigned long __trbe_normal_offset(struct perf_output_handle *handle)
>>   	 * trbe_base				trbe_base + nr_pages
>>   	 *
>>   	 * Perf aux buffer does not have any space for the driver to write into.
>> -	 * Just communicate trace truncation event to the user space by marking
>> -	 * it with PERF_AUX_FLAG_TRUNCATED.
>>   	 */
>> -	if (!handle->size) {
>> -		perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED);
>> +	if (!handle->size)
>>   		return 0;
>> -	}
>>   
>>   	/* Compute the tail and wakeup indices now that we've aligned head */
>>   	tail = PERF_IDX2OFF(handle->head + handle->size, buf);
>> @@ -361,7 +357,6 @@ static unsigned long __trbe_normal_offset(struct perf_output_handle *handle)
>>   		return limit;
>>   
>>   	trbe_pad_buf(handle, handle->size);
>> -	perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED);
>>   	return 0;
>>   }
> 
> What about in trbe_handle_spurious() path which used to set the flag via
> compute_trbe_buffer_limit(), but would not any more after this change. I
> guess following additional change would be required to preserve the past
> behaviour.
> 
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -685,6 +685,7 @@ static void trbe_handle_spurious(struct perf_output_handle *handle)
>          buf->trbe_write = buf->trbe_base + PERF_IDX2OFF(handle->head, buf);
>          if (buf->trbe_limit == buf->trbe_base) {
>                  trbe_drain_and_disable_local();
> +               perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED);
>                  return;
>          }
>          trbe_enable_hw(buf);
> 

Agreed, I will add this.

Thanks
Suzuki