On 8/27/24 9:48 PM, Akhil P Oommen wrote:
On Fri, Aug 23, 2024 at 10:23:48AM +0100, Connor Abbott wrote:
On Fri, Aug 23, 2024 at 10:21 AM Connor Abbott <cwabbott0@xxxxxxxxx> wrote:
On Thu, Aug 22, 2024 at 9:06 PM Akhil P Oommen <quic_akhilpo@xxxxxxxxxxx> wrote:
On Wed, Aug 21, 2024 at 05:02:56PM +0100, Connor Abbott wrote:
On Mon, Aug 19, 2024 at 9:09 PM Akhil P Oommen <quic_akhilpo@xxxxxxxxxxx> wrote:
On Thu, Aug 15, 2024 at 08:26:14PM +0200, Antonino Maniscalco wrote:
This patch implements preemption feature for A6xx targets, this allows
the GPU to switch to a higher priority ringbuffer if one is ready. A6XX
hardware as such supports multiple levels of preemption granularities,
ranging from coarse grained(ringbuffer level) to a more fine grained
such as draw-call level or a bin boundary level preemption. This patch
enables the basic preemption level, with more fine grained preemption
support to follow.
Signed-off-by: Sharat Masetty <smasetty@xxxxxxxxxxxxxx>
Signed-off-by: Antonino Maniscalco <antomani103@xxxxxxxxx>
---
No postamble packets which resets perfcounters? It is necessary. Also, I
think we should disable preemption during profiling like we disable slumber.
-Akhil.
I don't see anything in kgsl which disables preemption during
profiling. It disables resetting perfcounters when doing system-wide
profiling, like freedreno, and in that case I assume preempting is
fine because the system profiler has a complete view of everything and
should "see" preemptions through the traces. For something like
VK_KHR_performance_query I suppose we'd want to disable preemption
because we disable saving/restoring perf counters, but that has to
happen in userspace because the kernel doesn't know what userspace
does.
KGSL does some sort of arbitration of perfcounter configurations and
adds the select/enablement reg configuration as part of dynamic
power up register list which we are not doing here. Is this something
you are taking care of from userspace via preamble?
-Akhil
I don't think we have to take care of that in userspace, because Mesa
will always configure the counter registers before reading them in the
same submission, and if it gets preempted in the meantime then we're
toast anyways (due to not saving/restoring perf counters). kgsl sets
them from userspace, which is why it has to do something to set them
Sorry, should be "kgsl sets them from the kernel".
after IFPC slumber or a context switch when the HW state is gone.
Also, because the upstream approach doesn't play nicely with system
profilers like perfetto, VK_KHR_performance_query is hidden by default
behind a debug flag in turnip. So there's already an element of "this
is unsupported, you have to know what you're doing to use it."
But when you have composition on GPU enabled, there will be very frequent
preemption. And I don't know how usable profiling tools will be in that
case unless you disable preemption with a Mesa debug flag. But for that
to work, all existing submitqueues should be destroyed and recreated.
So I was thinking that we can use the sysprof propertry to force L0
preemption from kernel.
-Akhil.
Right but when using a system profiler I imagined the expectation would
be to be able to understand how applications and compositor interact. An
use case could be measuring latency and understanding what contributes
to it. That is actually the main reason I added traces for preemption.
Disabling preemption would make it less useful for this type of
analysis. Did you have an use case in mind for a system profiler that
would benefit from disabling preemption and that is not covered by
VK_KHR_performance_query (or equivalent GL ext)?
Best regards,
--
Antonino Maniscalco <antomani103@xxxxxxxxx>
