Nouveau fences?

[Francisco Jerez]

Francisco Jerez <currojerez at riseup.net> writes:

> Thomas Hellstrom <thomas at shipmail.org> writes:
>
>> Ben,
>>
>> I'm looking at a way to make TTM memory management asynchronous with
>> the CPU. The idea is that you should basically be able to DMA data to
>> and from memory regions without waiting for idle, as long as the GPU
>> has a means to provide operation ordering.
>>
> Sounds good. I guess you're mainly dealing with BO eviction
> synchronization? The only problem I see on our side is that calls to our
> move() hook aren't guaranteed to be carried out in order (because of the
> multiple hardware channels). I'm thinking that move() could be extended
> with an optional sync_obj argument, that way move() would be able to
> make sure that evictions are strictly ordered with respect to the fence
> specified.
>
>> While doing that I looked a bit at the Nouveau fencing. It appears
>> like waiting for fences is polling only (no irq to signal fences)? Is
>> that correct?
>>
> That's right, nvidia hardware has no nice way to schedule a fence-like
> interrupt we could selectively turn on and off around the sync_obj_wait
> hook. There's a bunch of (more or less) chipset-specific hacks that
> could be used to get an equivalent effect, but polling has seemed good
> enough so far (in the typical case we only take the "lazy" path so CPU
> usage is still OK).
>
> Unconditional PFIFO CACHE interrupts might be an option too, but, I'm a
> bit afraid of the PFIFO stalls and useless IRQ storms some applications
> could trigger.
>
Meh, apparently this one couldn't make it through, some spam filter has
decided I'm a spammer for some reason...

>> /Thomas
>>
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