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

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Date:   Thu, 21 Sep 2023 11:14:27 +0100
From:   Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
To:     Adrián Larumbe <adrian.larumbe@...labora.com>,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de, airlied@...il.com, daniel@...ll.ch,
        robdclark@...il.com, quic_abhinavk@...cinc.com,
        dmitry.baryshkov@...aro.org, sean@...rly.run,
        marijn.suijten@...ainline.org, robh@...nel.org,
        steven.price@....com
Cc:     linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, healych@...zon.com,
        Boris Brezillon <boris.brezillon@...labora.com>,
        kernel@...labora.com, freedreno@...ts.freedesktop.org
Subject: Re: [PATCH v6 6/6] drm/drm-file: Show finer-grained BO sizes in
 drm_show_memory_stats


On 20/09/2023 16:32, Tvrtko Ursulin wrote:
> 
> 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@...labora.com>
>> Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>
>> Reviewed-by: Steven Price <steven.price@....com>
>> ---
>>   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.

FWIW both current and the threshold option make testing the feature very 
annoying.

So I'd really propose we simply use smaller unit when unaligned.

Regards,

Tvrtko