Re: [Intel-gfx] [PATCH] drm/i915/mtl: Connect root sysfs entries to GT0

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 13/01/2023 03:15, Dixit, Ashutosh wrote:
> On Thu, 12 Jan 2023 18:27:52 -0800, Vinay Belgaumkar wrote:
>>
>> Reading current root sysfs entries gives a min/max of all
>> GTs. Updating this so we return default (GT0) values when root
>> level sysfs entries are accessed, instead of min/max for the card.
>> Tests that are not multi GT capable will read incorrect sysfs
>> values without this change on multi-GT platforms like MTL.
>>
>> Fixes: a8a4f0467d70 ("drm/i915: Fix CFI violations in gt_sysfs")
> 
> We seem to be proposing to change the previous sysfs ABI with this patch?
> But even then it doesn't seem correct to use gt0 values for device level
> sysfs. Actually I received the following comment about using max freq
> across gt's for device level freq's (gt_act_freq_mhz etc.) from one of our
> users:
> 
> -----
> On Sun, 06 Nov 2022 08:54:04 -0800, Lawson, Lowren H wrote:
> 
> Why show maximum? Wouldn’t average be more accurate to the user experience?
> 
> As a user, I expect the ‘card’ frequency to be relatively accurate to the
> entire card. If I see 1.6GHz, but the card is behaving as if it’s running a
> 1.0 & 1.6GHz on the different compute tiles, I’m going to see a massive
> decrease in compute workload performance while at ‘maximum’ frequency.
> -----
> 
> So I am not sure why max/min were previously chosen. Why not the average?

I think we still have time to just either stop exposing the global files 
on multi-tile platforms (all are under force probe), or return some 
error from them.

IMO it's not kernel's job to provide any representation here - be in 
min, max, sum or average (different "blending" methods were discussed 
for different files) - all of them have some potential to be misleading 
from different angles.

Regards,

Tvrtko