Re: [PATCH 0/4] drm/panfrost: Plumb cycle counters to userspace

[Tomeu Vizoso <tomeu.vizoso@collabora.com>]

Hi Alyssa,

Will this be enough to implement GL_TIMESTAMP and GL_TIME_ELAPSED queries?

Guess the DDK implements these as WRITE_VALUE jobs, and there's also a 
soft job BASE_JD_REQ_SOFT_DUMP_CPU_GPU_TIME that I guess is used for 
glGet*(GL_TIMESTAMP). Other DRM drivers use an ioctl for that instead.

Regards,

Tomeu

On 5/27/21 10:38 PM, alyssa.rosenzweig@collabora.com wrote:
> From: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
> 
> Mali has hardware cycle counters (and GPU timestamps) available for
> profiling. These are exposed in various ways:
> 
> - Kernel: As CYCLE_COUNT and TIMESTAMP registers
> - Job chain: As WRITE_VALUE descriptors
> - Shader (Midgard): As LD_SPECIAL selectors
> - Shader (Bifrost): As the LD_GCLK.u64 instruction
> 
> These form building blocks for profiling features, for example the
> ARB_shader_clock extension which accesses the counters from an
> application's shader.
> 
> The counters consume power, so it is recommended to disable the counters
> when not in use. To do so, we follow the strategy from mali_kbase: add a
> counter requirement to the job, start the counters only when required,
> and stop them as quickly as possible.
> 
> The new UABI will be used in Mesa. An implementation of ARB_shader_clock
> using this UABI is available as a pending upstream merge request [1].
> The implementation passes the relevant piglit test, validating both the
> kernel and mesa.
> 
> The main outstanding questing is the proper name. Performance monitoring
> ("PERMON") is the name used by kbase, but it's jargon-y and risks
> confusion with performance counters, an orthogonal mechanism. Cycle
> count is more descriptive and matches the actual hardware name, but
> obscures that the same mechanism is required for GPU timestamps. This
> bit of bikeshedding aside, I'm pleased with the patches.
> 
> [1] https://gitlab.freedesktop.org/mesa/mesa/merge_requests/11051
> 
> Alyssa Rosenzweig (4):
>    drm/panfrost: Add cycle counter job requirement
>    drm/panfrost: Add CYCLE_COUNT_START/STOP commands
>    drm/panfrost: Add permon acquire/release helpers
>    drm/panfrost: Handle PANFROST_JD_REQ_PERMON
> 
>   drivers/gpu/drm/panfrost/panfrost_device.h |  3 +++
>   drivers/gpu/drm/panfrost/panfrost_drv.c    | 10 +++++++---
>   drivers/gpu/drm/panfrost/panfrost_gpu.c    | 20 ++++++++++++++++++++
>   drivers/gpu/drm/panfrost/panfrost_gpu.h    |  3 +++
>   drivers/gpu/drm/panfrost/panfrost_job.c    |  6 ++++++
>   drivers/gpu/drm/panfrost/panfrost_regs.h   |  2 ++
>   include/uapi/drm/panfrost_drm.h            |  3 ++-
>   7 files changed, 43 insertions(+), 4 deletions(-)
>