On 16/02/2024 16:57, Daniel Vetter wrote:
On Wed, Feb 14, 2024 at 01:52:05PM +0000, Steven Price wrote:
Hi Adrián,
On 14/02/2024 12:14, Adrián Larumbe wrote:
A driver user expressed interest in being able to access engine usage stats
through fdinfo when debugfs is not built into their kernel. In the current
implementation, this wasn't possible, because it was assumed even for
inflight jobs enabling the cycle counter and timestamp registers would
incur in additional power consumption, so both were kept disabled until
toggled through debugfs.
A second read of the TRM made me think otherwise, but this is something
that would be best clarified by someone from ARM's side.
I'm afraid I can't give a definitive answer. This will probably vary
depending on implementation. The command register enables/disables
"propagation" of the cycle/timestamp values. This propagation will cost
some power (gates are getting toggled) but whether that power is
completely in the noise of the GPU as a whole I can't say.
The out-of-tree kbase driver only enables the counters for jobs
explicitly marked (BASE_JD_REQ_PERMON) or due to an explicit connection
from a profiler.
I'd be happier moving the debugfs file to sysfs rather than assuming
that the power consumption is small enough for all platforms.
Ideally we'd have some sort of kernel interface for a profiler to inform
the kernel what it is interested in, but I can't immediately see how to
make that useful across different drivers. kbase's profiling support is
great with our profiling tools, but there's a very strong connection
between the two.
Yeah I'm not sure whether a magic (worse probably per-driver massively
different) file in sysfs is needed to enable gpu perf monitoring stats in
fdinfo.
I get that we do have a bit a gap because the linux perf pmu stuff is
global, and you want per-process, and there's kinda no per-process support
for perf stats for devices. But that's probably the direction we want to
go, not so much fdinfo. At least for hardware performance counters and
things like that.
Iirc the i915 pmu support had some integration for per-process support,
you might want to chat with Tvrtko for kernel side and Lionel for more
userspace side. At least if I'm not making a complete mess and my memory
is vaguely related to reality. Adding them both.
Yeah there are two separate things, i915 PMU and i915 Perf/OA.
If my memory serves me right I indeed did have a per-process support for
i915 PMU implemented as an RFC (or at least a branch somewhere) some
years back. IIRC it only exposed the per engine GPU utilisation and did
not find it very useful versus the complexity. (I think it at least
required maintaining a map of drm clients per task.)
Our more useful profiling is using a custom Perf/OA interface
(Observation Architecture) which is possibly similar to kbase mentioned
above. Why it is a custom interface is explained in a large comment on
top of i915_perf.c. Not sure if all of them still hold but on the
overall perf does not sound like the right fit for detailed GPU profiling.
Also PMU drivers are very challenging to get the implementation right,
since locking model and atomicity requirements are quite demanding.
From my point of view, at least it is my initial thinking, if custom
per driver solutions are strongly not desired, it could be interesting
to look into whether there is enough commonality, in at least concepts,
to see if a new DRM level common but extensible API would be doable.
Even then it may be tricky to "extract" enough common code to justify it.
Regards,
Tvrtko
Cheers, Sima
Steve
Adrián Larumbe (1):
drm/panfrost: Always record job cycle and timestamp information
drivers/gpu/drm/panfrost/Makefile | 2 --
drivers/gpu/drm/panfrost/panfrost_debugfs.c | 21 ------------------
drivers/gpu/drm/panfrost/panfrost_debugfs.h | 14 ------------
drivers/gpu/drm/panfrost/panfrost_device.h | 1 -
drivers/gpu/drm/panfrost/panfrost_drv.c | 5 -----
drivers/gpu/drm/panfrost/panfrost_job.c | 24 ++++++++-------------
drivers/gpu/drm/panfrost/panfrost_job.h | 1 -
7 files changed, 9 insertions(+), 59 deletions(-)
delete mode 100644 drivers/gpu/drm/panfrost/panfrost_debugfs.c
delete mode 100644 drivers/gpu/drm/panfrost/panfrost_debugfs.h
base-commit: 6b1f93ea345947c94bf3a7a6e668a2acfd310918
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
