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SubjectRe: [PATCH v2 09/10] coresight: trbe: End the AUX handle on truncation
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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@arm.com>
> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> Cc: Mike Leach <mike.leach@linaro.org>
> Cc: Leo Yan <leo.yan@linaro.org>
> Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: Will Deacon <will@kernel.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.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@arm.com>

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