Re: [PATCH v3 1/3] drm/panthor: Add tracepoints for cache flushing

[Boris Brezillon <boris.brezillon@collabora.com>]

On Tue, 11 Aug 2026 16:08:31 +0200
Nicolas Frattaroli <nicolas.frattaroli@collabora.com> wrote:

> Add two new event tracepoints: gpu_cache_flush_start to be emitted after
> acquiring the flush mutex and reqs spinlock, and gpu_cache_flush_end to
> be emitted when leaving the function.
> 
> This allows debugging the duration a flush takes irrespective of initial
> function entry lock contention by subtracting the start tracepoint's
> timestamp from the end tracepoint timestamp, and additionally contains
> information such as which caches were flushed.
> 
> Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
> Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
> Reviewed-by: Steven Price <steven.price@arm.com>
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> ---
>  drivers/gpu/drm/panthor/panthor_gpu.c   |  7 ++++-
>  drivers/gpu/drm/panthor/panthor_trace.h | 49 +++++++++++++++++++++++++++++++++
>  2 files changed, 55 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_gpu.c b/drivers/gpu/drm/panthor/panthor_gpu.c
> index c013d6bf9a59..68e2dd2527df 100644
> --- a/drivers/gpu/drm/panthor/panthor_gpu.c
> +++ b/drivers/gpu/drm/panthor/panthor_gpu.c
> @@ -337,6 +337,7 @@ int panthor_gpu_flush_caches(struct panthor_device *ptdev,
>  	guard(mutex)(&ptdev->gpu->cache_flush_lock);
>  
>  	spin_lock_irqsave(&ptdev->gpu->reqs_lock, flags);
> +	trace_gpu_cache_flush_start(ptdev->base.dev, l2, lsc, other);
>  	if (!(ptdev->gpu->pending_reqs & GPU_IRQ_CLEAN_CACHES_COMPLETED)) {
>  		ptdev->gpu->pending_reqs |= GPU_IRQ_CLEAN_CACHES_COMPLETED;
>  		gpu_write(gpu->iomem, GPU_CMD, GPU_FLUSH_CACHES(l2, lsc, other));
> @@ -345,8 +346,10 @@ int panthor_gpu_flush_caches(struct panthor_device *ptdev,
>  	}
>  	spin_unlock_irqrestore(&ptdev->gpu->reqs_lock, flags);
>  
> -	if (ret)
> +	if (ret) {
> +		trace_gpu_cache_flush_end(ptdev->base.dev, l2, lsc, other);

I don't mind having start/end traces, but I still think it'd be
valuable to report failure cases.

>  		return ret;
> +	}
>  
>  	if (!wait_event_timeout(ptdev->gpu->reqs_acked,
>  				!(ptdev->gpu->pending_reqs & GPU_IRQ_CLEAN_CACHES_COMPLETED),
> @@ -360,6 +363,8 @@ int panthor_gpu_flush_caches(struct panthor_device *ptdev,
>  		spin_unlock_irqrestore(&ptdev->gpu->reqs_lock, flags);
>  	}
>  
> +	trace_gpu_cache_flush_end(ptdev->base.dev, l2, lsc, other);
> +
>  	if (ret) {
>  		panthor_device_schedule_reset(ptdev);
>  		drm_err(&ptdev->base, "Flush caches timeout");
> diff --git a/drivers/gpu/drm/panthor/panthor_trace.h b/drivers/gpu/drm/panthor/panthor_trace.h
> index 6ffeb4fe6599..6951b95b1de7 100644
> --- a/drivers/gpu/drm/panthor/panthor_trace.h
> +++ b/drivers/gpu/drm/panthor/panthor_trace.h
> @@ -76,6 +76,55 @@ TRACE_EVENT(gpu_job_irq,
>  		  __entry->events, __entry->duration_ns)
>  );
>  
> +DECLARE_EVENT_CLASS(gpu_cache_flush_template,
> +	TP_PROTO(const struct device *dev, u32 l2, u32 lsc, u32 other),
> +	TP_ARGS(dev, l2, lsc, other),
> +	TP_STRUCT__entry(
> +		__string(dev_name, dev_name(dev))
> +		__field(u32, l2)
> +		__field(u32, lsc)
> +		__field(u32, other)
> +	),
> +	TP_fast_assign(
> +		__assign_str(dev_name);
> +		__entry->l2     = l2;
> +		__entry->lsc    = lsc;
> +		__entry->other  = other;
> +	),
> +	TP_printk("%s: l2=0x%x lsc=0x%x other=0x%x", __get_str(dev_name),
> +		  __entry->l2, __entry->lsc, __entry->other)
> +);
> +
> +/**
> + * gpu_cache_flush_start - called after cache flush locks taken, before flush
> + * @dev: pointer to the &struct device, for printing the device name
> + * @l2: "l2" flush flags
> + * @lsc: "lsc" flush flags
> + * @other: "other" flush flags
> + *
> + * Fires after any initial lock contention around the locks needed for flushing
> + * caches, but before the actual cache flush is requested.
> + */
> +DEFINE_EVENT(gpu_cache_flush_template, gpu_cache_flush_start,
> +	     TP_PROTO(const struct device *dev, u32 l2, u32 lsc, u32 other),
> +	     TP_ARGS(dev, l2, lsc, other)
> +);
> +
> +/**
> + * gpu_cache_flush_end - called after cache flush
> + * @dev: pointer to the &struct device, for printing the device name
> + * @l2: "l2" flush flags
> + * @lsc: "lsc" flush flags
> + * @other: "other" flush flags
> + *
> + * Fires after either the cache flush is complete, or has failed. Can be used
> + * together with gpu_cache_flush_start to get how long the flush has taken.
> + */
> +DEFINE_EVENT(gpu_cache_flush_template, gpu_cache_flush_end,
> +	     TP_PROTO(const struct device *dev, u32 l2, u32 lsc, u32 other),
> +	     TP_ARGS(dev, l2, lsc, other)
> +);
> +
>  #endif /* __PANTHOR_TRACE_H__ */
>  
>  #undef TRACE_INCLUDE_PATH
>