[PATCH 0/7] Per client engine busyness

[Tvrtko Ursulin]

On 14/05/2021 14:53, Christian König wrote:
>>
>> David also said that you considered sysfs but were wary of exposing 
>> process info in there. To clarify, my patch is not exposing sysfs 
>> entry per process, but one per open drm fd.
>>
> 
> Yes, we discussed this as well, but then rejected the approach.
> 
> To have useful information related to the open drm fd you need to 
> related that to process(es) which have that file descriptor open. Just 
> tracking who opened it first like DRM does is pretty useless on modern 
> systems.

We do update the pid/name for fds passed over unix sockets.

> But an "lsof /dev/dri/renderD128" for example does exactly what top does 
> as well, it iterates over /proc and sees which process has that file open.

Lsof is quite inefficient for this use case. It has to open _all_ open 
files for _all_ processes on the system to find a handful of ones which 
may have the DRM device open.

> So even with sysfs aid for discovery you are back to just going over all 
> files again.

For what use case?

To enable GPU usage in top we can do much better than iterate over all 
open files in the system. We can start with a process if going with the 
/proc proposal, or with the opened DRM file directly with the sysfs 
proposal. Both are significantly fewer than total number of open files 
across all processes.

Regards,

Tvrtko