On 6/25/20 2:11 AM, Dmitry Osipenko wrote:
23.06.2020 15:09, Mikko Perttunen пишет:
/* Command is an opcode gather from a GEM handle */
#define DRM_TEGRA_SUBMIT_COMMAND_GATHER 0
/* Command is an opcode gather from a user pointer */
#define DRM_TEGRA_SUBMIT_COMMAND_GATHER_UPTR 1
I'm a bit dubious about whether we really need to retain the non-UPTR
variant. The memory-copying overhead is negligible because cmdstream's
data usually is hot in CPU's cache
IIRC, the most (if not all) of the modern DRM drivers drivers use the
usrptr-only for the cmdstream.
At least there is no any real-world userspace example today that could
benefit from a non-UPTR variant.
I'm suggesting to leave out the non-UPTR gather variant for now, keeping
it in mind as a potential future extension of the submission UAPI. Any
objections?
Sure, we should be able to drop it. Downstream userspace is using it,
but we should be able to fix that. I was thinking that we can directly
map the user pages and point the gather to them without copying - that
way we wouldn't need to make DMA allocations inside the driver for every
submit. (On early Tegras we could just copy into the pushbuffer but that
won't work for newer ones).
Mikko
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