Re: [PATCH v4 00/38] GPU scheduler for i915 driver

John Harrison
2016-01-12T11:43:12Z

On 12/01/2016 04:37, Tian, Kevin wrote:
>> From: John.C.Harrison@Intel.com
>> Sent: Tuesday, January 12, 2016 2:42 AM
>>
>> From: John Harrison <John.C.Harrison@Intel.com>
>>
>> Implemented a batch buffer submission scheduler for the i915 DRM driver.
>>
>> The general theory of operation is that when batch buffers are
>> submitted to the driver, the execbuffer() code assigns a unique seqno
>> value and then packages up all the information required to execute the
>> batch buffer at a later time. This package is given over to the
>> scheduler which adds it to an internal node list. The scheduler also
>> scans the list of objects associated with the batch buffer and
>> compares them against the objects already in use by other buffers in
>> the node list. If matches are found then the new batch buffer node is
>> marked as being dependent upon the matching node. The same is done for
>> the context object. The scheduler also bumps up the priority of such
>> matching nodes on the grounds that the more dependencies a given batch
>> buffer has the more important it is likely to be.
>>
> A curious question. Is this new GPU scheduler still useful when GuC
> is enabled? Sorry if this Q. has been answered before.
Yes. The scheduler works with any back end submission mechanism - legacy
ring buffer, execlist or Guc. Indeed, the pre-emption support (next
patch series in the set) currently requires the GuC. Execlist support is
possible but just not currently planned due to time constraints. Legacy
ring buffer pre-emption is very different and a lot more work for very
little benefit - pre-execlist hardware does not support very much in the
way of pre-emption facilities.

The GuC itself does not really do much in the way of scheduling. It does
know about the dependencies between batch buffers, for example, so
cannot re-order work according to priority. Adding such support without
still having large chunks of kernel driver support is a currently
unscoped and unplanning task.

>
> Thanks
> Kevin