[RFC PATCH 1/8] tracing/gpu: modify gpu_mem_total

[Daniel Vetter]

On Wed, Oct 20, 2021 at 08:10:20PM -0700, Gurchetan Singh wrote:
> The existing gpu_mem_total tracepoint [1] is not currently used by
> any in-tree consumers, we should add some.
> 
> In addition, there's a desire to report imported memory via the
> counters too [2].
> 
> To do this, we'll have to redefine the event to:
> 
> a) Change 'pid' to 'ctx_id'
> 
> The reason is  DRM subsystem is created with GEM objects, DRM devices
> and DRM files in mind.  A GEM object is associated with DRM device,
> and it may be shared between one or more DRM files.
> 
> Per-instance (or "context") counters make more sense than per-process
> counters for DRM.  For GPUs that per process counters (kgsl), this
> change is backwards compatible.
> 
> b) add an "import_mem_total" field
> 
> We're just appending a field, so no problem here.  Change "size" to
> "mem_total" as well (name changes are backwards compatible).
> 
> [1] https://lore.kernel.org/r/20200302234840.57188-1-zzyiwei@google.com/
> [2] https://www.spinics.net/lists/kernel/msg4062769.html
> 
> Signed-off-by: Gurchetan Singh <gurchetansingh at chromium.org>

Yay, that patch is just impressive. Lands a new gpu tracepoints, never
even showed up on the gpu subsystem discussion list.

Imo just delete this and start over with something proper, that's actually
used by drivers.
-Daniel

> ---
>  include/trace/events/gpu_mem.h | 61 ++++++++++++++++++++++++----------
>  1 file changed, 43 insertions(+), 18 deletions(-)
> 
> diff --git a/include/trace/events/gpu_mem.h b/include/trace/events/gpu_mem.h
> index 26d871f96e94..198b87f50356 100644
> --- a/include/trace/events/gpu_mem.h
> +++ b/include/trace/events/gpu_mem.h
> @@ -14,41 +14,66 @@
>  #include <linux/tracepoint.h>
>  
>  /*
> - * The gpu_memory_total event indicates that there's an update to either the
> - * global or process total gpu memory counters.
> + * The gpu_mem_total event indicates that there's an update to local or
> + * global gpu memory counters.
>   *
> - * This event should be emitted whenever the kernel device driver allocates,
> - * frees, imports, unimports memory in the GPU addressable space.
> + * This event should be emitted whenever a GPU device (ctx_id == 0):
>   *
> - * @gpu_id: This is the gpu id.
> + *   1) allocates memory.
> + *   2) frees memory.
> + *   3) imports memory from an external exporter.
>   *
> - * @pid: Put 0 for global total, while positive pid for process total.
> + * OR when a GPU device instance (ctx_id != 0):
>   *
> - * @size: Size of the allocation in bytes.
> + *   1) allocates or acquires a reference to memory from another instance.
> + *   2) frees or releases a reference to memory from another instance.
> + *   3) imports memory from another GPU device instance.
>   *
> + * When ctx_id == 0, both mem_total and import_mem_total total counters
> + * represent a global total.  When ctx_id == 0, these counters represent
> + * an instance specifical total.
> + *
> + * Note allocation does not necessarily mean backing the memory with pages.
> + *
> + * @gpu_id: unique ID of the GPU.
> + *
> + * @ctx_id: an ID for specific instance of the GPU device.
> + *
> + * @mem_total: - total size of memory known to a GPU device, including
> + *		 imports (ctx_id == 0)
> + *	       - total size of memory known to a GPU device instance
> + *		 (ctx_id != 0)
> + *
> + * @import_mem_total: - size of memory imported from outside GPU
> + *			device (ctx_id == 0)
> + *		      - size of memory imported into GPU device instance.
> + *			(ctx_id == 0)
>   */
>  TRACE_EVENT(gpu_mem_total,
>  
> -	TP_PROTO(uint32_t gpu_id, uint32_t pid, uint64_t size),
> +	TP_PROTO(u32 gpu_id, u32 ctx_id, u64 mem_total, u64 import_mem_total),
>  
> -	TP_ARGS(gpu_id, pid, size),
> +	TP_ARGS(gpu_id, ctx_id, mem_total, import_mem_total),
>  
>  	TP_STRUCT__entry(
> -		__field(uint32_t, gpu_id)
> -		__field(uint32_t, pid)
> -		__field(uint64_t, size)
> +		__field(u32, gpu_id)
> +		__field(u32, ctx_id)
> +		__field(u64, mem_total)
> +		__field(u64, import_mem_total)
>  	),
>  
>  	TP_fast_assign(
>  		__entry->gpu_id = gpu_id;
> -		__entry->pid = pid;
> -		__entry->size = size;
> +		__entry->ctx_id = ctx_id;
> +		__entry->mem_total = mem_total;
> +		__entry->import_mem_total = import_mem_total;
>  	),
>  
> -	TP_printk("gpu_id=%u pid=%u size=%llu",
> -		__entry->gpu_id,
> -		__entry->pid,
> -		__entry->size)
> +	TP_printk("gpu_id=%u, ctx_id=%u, mem total=%llu, mem import total=%llu",
> +		  __entry->gpu_id,
> +		  __entry->ctx_id,
> +		  __entry->mem_total,
> +		  __entry->import_mem_total)
>  );
>  
>  #endif /* _TRACE_GPU_MEM_H */
> -- 
> 2.25.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch