Re: [PATCH v5 2/9] gpu: nova-core: gsp: add mechanism to wait for space on command queue

["Eliot Courtney" <ecourtney@nvidia.com>]

On Wed Mar 4, 2026 at 8:39 PM JST, Danilo Krummrich wrote:
> On Wed Mar 4, 2026 at 2:42 AM CET, Eliot Courtney wrote:
>> +    fn allocate_command(&mut self, size: usize, timeout: Delta) -> Result<GspCommand<'_>> {
>> +        read_poll_timeout(
>> +            || Ok(self.driver_write_area_size()),
>> +            |available_bytes| *available_bytes >= size_of::<GspMsgElement>() + size,
>> +            Delta::ZERO,
>
> Isn't this either creating unneccessary thrashing of the memory controller or
> unnecessary contention at the cache-coherency level?
>
> I think we should probably add at least a small delay of something around 1us.

This is what nouveau does (specifically `usleep_range(1, 2)`). OTOH,
openrm just does a busy wait, which is what I replicated here for now.
GSP command queue not having space IIUC is meant to be very exceptional.
I am not sure which is best, maybe Alex has an opinion, but also happy
to change it because that reasoning makes sense to me and I don't know
enough about the distribution of how often it would actually need
to wait to know if 0 delay is justified.