On Mon, 25 Sep 2023 19:55:21 +0200 Christian König <christian.koenig@xxxxxxx> wrote: > Am 25.09.23 um 14:55 schrieb Boris Brezillon: > > +The imagination team, who's probably interested too. > > > > On Mon, 25 Sep 2023 00:43:06 +0200 > > Danilo Krummrich <dakr@xxxxxxxxxx> wrote: > > > >> Currently, job flow control is implemented simply by limiting the amount > >> of jobs in flight. Therefore, a scheduler is initialized with a > >> submission limit that corresponds to a certain amount of jobs. > >> > >> This implies that for each job drivers need to account for the maximum > >> job size possible in order to not overflow the ring buffer. > >> > >> However, there are drivers, such as Nouveau, where the job size has a > >> rather large range. For such drivers it can easily happen that job > >> submissions not even filling the ring by 1% can block subsequent > >> submissions, which, in the worst case, can lead to the ring run dry. > >> > >> In order to overcome this issue, allow for tracking the actual job size > >> instead of the amount job jobs. Therefore, add a field to track a job's > >> submission units, which represents the amount of units a job contributes > >> to the scheduler's submission limit. > > As mentioned earlier, this might allow some simplifications in the > > PowerVR driver where we do flow-control using a dma_fence returned > > through ->prepare_job(). The only thing that'd be missing is a way to > > dynamically query the size of a job (a new hook?), instead of having the > > size fixed at creation time, because PVR jobs embed native fence waits, > > and the number of native fences will decrease if some of these fences > > are signalled before ->run_job() is called, thus reducing the job size. > > Exactly that is a little bit questionable since it allows for the device > to postpone jobs infinitely. > > It would be good if the scheduler is able to validate if it's ever able > to run the job when it is pushed into the entity. Yes, we do that already. We check that the immutable part of the job (everything that's not a native fence wait) fits in the ringbuf.
