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SubjectRe: [PATCH 0/1] Always record job cycle and timestamp information
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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.

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


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