Re: [PATCH v6 6/6] drm/drm-file: Show finer-grained BO sizes in drm_show_memory_stats

[Tvrtko Ursulin]

On 20/09/2023 00:34, Adrián Larumbe wrote:
> The current implementation will try to pick the highest available size
> display unit as soon as the BO size exceeds that of the previous
> multiplier. That can lead to loss of precision in contexts of low memory
> usage.
>
> The new selection criteria try to preserve precision, whilst also
> increasing the display unit selection threshold to render more accurate
> values.
>
> Signed-off-by: Adrián Larumbe <adrian.larumbe@xxxxxxxxxxxxx>
> Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> Reviewed-by: Steven Price <steven.price@xxxxxxx>
> ---
>   drivers/gpu/drm/drm_file.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
> index 762965e3d503..34cfa128ffe5 100644
> --- a/drivers/gpu/drm/drm_file.c
> +++ b/drivers/gpu/drm/drm_file.c
> @@ -872,6 +872,8 @@ void drm_send_event(struct drm_device *dev, struct drm_pending_event *e)
>   }
>   EXPORT_SYMBOL(drm_send_event);
>   
> +#define UPPER_UNIT_THRESHOLD 100
> +
>   static void print_size(struct drm_printer *p, const char *stat,
>   		       const char *region, u64 sz)
>   {
> @@ -879,7 +881,8 @@ static void print_size(struct drm_printer *p, const char *stat,
>   	unsigned u;
>   
>   	for (u = 0; u < ARRAY_SIZE(units) - 1; u++) {
> -		if (sz < SZ_1K)
> +		if ((sz & (SZ_1K - 1)) &&

IS_ALIGNED worth it at all?

> +		    sz < UPPER_UNIT_THRESHOLD * SZ_1K)
>   			break;

Excuse me for a late comment (I was away). I did not get what what is 
special about a ~10% threshold? Sounds to me just going with the lower 
unit, when size is not aligned to the higher one, would be better than 
sometimes precision-sometimes-not.

Regards,

Tvrtko

>   		sz = div_u64(sz, SZ_1K);
>   	}