Re: [PATCH v4 04/40] drm/sched: Add enqueue credit limit

[Danilo Krummrich <dakr@kernel.org>]

(Cc: Boris)

On Thu, May 15, 2025 at 12:22:18PM -0400, Connor Abbott wrote:
> For some context, other drivers have the concept of a "synchronous"
> VM_BIND ioctl which completes immediately, and drivers implement it by
> waiting for the whole thing to finish before returning.

Nouveau implements sync by issuing a normal async VM_BIND and subsequently
waits for the out-fence synchronously.

> But this
> doesn't work for native context, where everything has to be
> asynchronous, so we're trying a new approach where we instead submit
> an asynchronous bind for "normal" (non-sparse/driver internal)
> allocations and only attach its out-fence to the in-fence of
> subsequent submits to other queues.

This is what nouveau does and I think other drivers like Xe and panthor do this
as well.

> Once you do this then you need a
> limit like this to prevent memory usage from pending page table
> updates from getting out of control. Other drivers haven't needed this
> yet, but they will when they get native context support.

What are the cases where you did run into this, i.e. which application in
userspace hit this? Was it the CTS, some game, something else?