linux-kernel - Re: [PATCH v2 09/10] coresight: trbe: End the AUX handle on truncation

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Message-ID: <d7c68b50-1537-32d9-6803-cf0c5973c880@arm.com>
Date:   Fri, 30 Jul 2021 11:24:44 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Suzuki K Poulose <suzuki.poulose@....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, Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH v2 09/10] coresight: trbe: End the AUX handle on
 truncation



On 7/23/21 6:16 PM, Suzuki K Poulose wrote:
> When we detect that there isn't enough space left to start
> a meaningful session, we disable the TRBE, marking the buffer
> as TRUNCATED. But we delay the notification to the perf layer
> by perf_aux_output_end() until the event is scheduled out.

via the CoreSight PMU layer's stop event ?

> This will cause significant black outs in the trace. Now that
> the CoreSight PMU layer can handle a closed "AUX" handle
> properly, we can close the handle as soon as we detect the
> case, allowing the userspace to collect and re-enable the
> event.
> 
> Also, while in the IRQ handler, move the irq_work_run() after
> we have updated the handle, to make sure the "TRUNCATED" flag
> causes the event to be disabled as soon as possible.

Makes sense.

Minor nit. Commit message here should be reformatted to be expanded
upto 75 character width.

> 
> 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>
> Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
> Cc: Will Deacon <will@...nel.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
>  drivers/hwtracing/coresight/coresight-trbe.c | 25 ++++++++++++--------
>  1 file changed, 15 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> index 6d6aad171c72..e7567727e8fc 100644
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -134,6 +134,7 @@ static void trbe_stop_and_truncate_event(struct perf_output_handle *handle)
>  	trbe_drain_and_disable_local();
>  	perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED |
>  				     PERF_AUX_FLAG_CORESIGHT_FORMAT_RAW);
> +	perf_aux_output_end(handle, 0);
>  	*this_cpu_ptr(buf->cpudata->drvdata->handle) = NULL;
>  }
>  
> @@ -699,7 +700,7 @@ static void trbe_handle_spurious(struct perf_output_handle *handle)
>  	isb();
>  }
>  
> -static void trbe_handle_overflow(struct perf_output_handle *handle)
> +static int trbe_handle_overflow(struct perf_output_handle *handle)
>  {
>  	struct perf_event *event = handle->event;
>  	struct trbe_buf *buf = etm_perf_sink_config(handle);
> @@ -728,10 +729,10 @@ static void trbe_handle_overflow(struct perf_output_handle *handle)
>  		 */
>  		trbe_drain_and_disable_local();
>  		*this_cpu_ptr(buf->cpudata->drvdata->handle) = NULL;
> -		return;
> +		return -EINVAL;
>  	}
>  
> -	__arm_trbe_enable(buf, handle);
> +	return __arm_trbe_enable(buf, handle);
>  }
>  
>  static bool is_perf_trbe(struct perf_output_handle *handle)
> @@ -762,6 +763,7 @@ static irqreturn_t arm_trbe_irq_handler(int irq, void *dev)
>  	struct perf_output_handle *handle = *handle_ptr;
>  	enum trbe_fault_action act;
>  	u64 status;
> +	bool truncated = false;
>  
>  	/* Reads to TRBSR_EL1 is fine when TRBE is active */
>  	status = read_sysreg_s(SYS_TRBSR_EL1);
> @@ -786,24 +788,27 @@ static irqreturn_t arm_trbe_irq_handler(int irq, void *dev)
>  	if (!is_perf_trbe(handle))
>  		return IRQ_NONE;
>  
> -	/*
> -	 * Ensure perf callbacks have completed, which may disable
> -	 * the trace buffer in response to a TRUNCATION flag.
> -	 */
> -	irq_work_run();
> -
>  	act = trbe_get_fault_act(status);
>  	switch (act) {
>  	case TRBE_FAULT_ACT_WRAP:
> -		trbe_handle_overflow(handle);
> +		truncated = !!trbe_handle_overflow(handle);
>  		break;
>  	case TRBE_FAULT_ACT_SPURIOUS:
>  		trbe_handle_spurious(handle);
>  		break;
>  	case TRBE_FAULT_ACT_FATAL:
>  		trbe_stop_and_truncate_event(handle);
> +		truncated = true;
>  		break;
>  	}
> +
> +	/*
> +	 * If the buffer was truncated, ensure perf callbacks
> +	 * have completed, which will disable the event.
> +	 */
> +	if (truncated)
> +		irq_work_run();
> +
>  	return IRQ_HANDLED;
>  }
>  
> 

LGTM.

Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>