Am 14.05.21 um 17:03 schrieb Tvrtko Ursulin:
On 14/05/2021 15:56, Christian König wrote:
Am 14.05.21 um 16:47 schrieb 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.
Well I just double checked and that is not correct.
Could be that i915 has some special code for that, but on my laptop I
only see the X server under the "clients" debugfs file.
Yes we have special code in i915 for this. Part of this series we are
discussing here.
Ah, yeah you should mention that. Could we please separate that into
common code instead? Cause I really see that as a bug in the current
handling independent of the discussion here.
As far as I know all IOCTLs go though some common place in DRM anyway.
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.
Completely agree.
The key point is you either need to have all references to an open
fd, or at least track whoever last used that fd.
At least the last time I looked even the fs layer didn't know which
fd is open by which process. So there wasn't really any alternative
to the lsof approach.
I asked you about the use case you have in mind which you did not
answer. Otherwise I don't understand when do you need to walk all
files. What information you want to get?
Per fd debugging information, e.g. instead of the top use case you know
which process you want to look at.
For the use case of knowing which DRM file is using how much GPU time
on engine X we do not need to walk all open files either with my sysfs
approach or the proc approach from Chris. (In the former case we
optionally aggregate by PID at presentation time, and in the latter
case aggregation is implicit.)
I'm unsure if we should go with the sysfs, proc or some completely
different approach.
In general it would be nice to have a way to find all the fd references
for an open inode.
Regards,
Christian.
Regards,
Tvrtko
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