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Message-ID: <8d9ad64b-a5f7-4a44-a557-7edb83322fdf@arm.com>
Date: Tue, 1 Apr 2025 13:51:36 +0100
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Leo Yan <leo.yan@....com>, Mike Leach <mike.leach@...aro.org>,
James Clark <james.clark@...aro.org>, Jonathan Corbet <corbet@....net>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 5/6] coresight: perf: Update buffer on AUX pause
On 11/03/2025 17:04, Leo Yan wrote:
> Due to sinks like ETR and ETB don't support interrupt handling, the
> hardware trace data might be lost for continuous running tasks.
>
> This commit takes advantage of the AUX pause for updating trace buffer
> to mitigate the trace data losing issue.
>
> The per CPU sink has its own interrupt handling. Thus, there will be a
> race condition between the updating buffer in NMI and sink's interrupt
> handler. To avoid the race condition, this commit disallows updating
> buffer on AUX pause for the per CPU sink. Currently, this is only
> applied for TRBE.
>
> Signed-off-by: Leo Yan <leo.yan@....com>
> ---
> .../hwtracing/coresight/coresight-etm-perf.c | 43 ++++++++++++++++++-
> 1 file changed, 41 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> index 2dcf1809cb7f..f1551c08ecb2 100644
> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> @@ -574,14 +574,53 @@ static void etm_event_start(struct perf_event *event, int flags)
> return;
> }
>
> -static void etm_event_pause(struct coresight_device *csdev,
> +static void etm_event_pause(struct perf_event *event,
> + struct coresight_device *csdev,
> struct etm_ctxt *ctxt)
> {
> + int cpu = smp_processor_id();
> + struct coresight_device *sink;
> + struct perf_output_handle *handle = &ctxt->handle;
> + struct coresight_path *path;
> + unsigned long size;
> +
> if (!ctxt->event_data)
> return;
>
> /* Stop tracer */
> coresight_pause_source(csdev);
> +
> + path = etm_event_cpu_path(ctxt->event_data, cpu);
> + sink = coresight_get_sink(path);
> + if (WARN_ON_ONCE(!sink))
> + return;
> +
> + /*
> + * The per CPU sink has own interrupt handling, it might have
> + * race condition with updating buffer on AUX trace pause if
> + * it is invoked from NMI. To avoid the race condition,
> + * disallows updating buffer for the per CPU sink case.
> + */
> + if (coresight_is_percpu_sink(sink))
> + return;
> +
> + if (WARN_ON_ONCE(handle->event != event))
> + return;
> +
> + if (!sink_ops(sink)->update_buffer)
> + return;
> +
> + size = sink_ops(sink)->update_buffer(sink, handle,
> + ctxt->event_data->snk_config);
I believe we keep the sink disabled/stopped in update_buffer. We need to
turn it back ON after the "buffer update". May be we could use a flag
to update_buffer() to indicate this is "pause" triggered update.
Cheers
Suzuki
> + if (READ_ONCE(handle->event)) {
> + if (!size)
> + return;
> +
> + perf_aux_output_end(handle, size);
> + perf_aux_output_begin(handle, event);
> + } else {
> + WARN_ON_ONCE(size);
> + }
> }
>
> static void etm_event_stop(struct perf_event *event, int mode)
> @@ -595,7 +634,7 @@ static void etm_event_stop(struct perf_event *event, int mode)
> struct coresight_path *path;
>
> if (mode & PERF_EF_PAUSE)
> - return etm_event_pause(csdev, ctxt);
> + return etm_event_pause(event, csdev, ctxt);
>
> /*
> * If we still have access to the event_data via handle,
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