On 2021/6/28 18:00, Bruce Richardson wrote: >> 4) The driver's ops design (here we only list key points): >> [dev_info_get]: mainly return the number of HW-queues >> [dev_configure]: nothing important >> [queue_setup]: create one virt-queue, has following main parameters: >> HW-queue-index: the HW-queue index used >> nb_desc: the number of HW descriptors >> opaque: driver's specific info >> Note1: this API return virt-queue index which will used in later >> API. >> If user want create multiple virt-queue one the same >> HW-queue, >> they could achieved by call queue_setup with the same >> HW-queue-index. >> Note2: I think it's hard to define queue_setup config paramter, and >> also this is control API, so I think it's OK to use opaque >> pointer to implement it. > I'm not sure opaque pointer will work in practice, so I think we should try > and standardize the parameters as much as possible. Since it's a control > plane API, using a struct with a superset of parameters may be workable. > Let's start with a minimum set and build up from there.
I tried to standardize a few parameters, which you can see on the new patch >> uint16_t rte_dmadev_completed(dev, vq_id, dma_cookie_t *cookie, >> uint16_t nb_cpls, bool *has_error) >> -- nb_cpls: indicate max process operations number >> -- has_error: indicate if there is an error >> -- return value: the number of successful completed operations. >> -- example: >> 1) If there are already 32 completed ops, and 4th is error, and >> nb_cpls is 32, then the ret will be 3(because 1/2/3th is OK), >> and >> has_error will be true. >> 2) If there are already 32 completed ops, and all successful >> completed, then the ret will be min(32, nb_cpls), and has_error >> will be false. >> 3) If there are already 32 completed ops, and all failed completed, >> then the ret will be 0, and has_error will be true. > +1 for this > >> uint16_t rte_dmadev_completed_status(dev_id, vq_id, dma_cookie_t >> *cookie, >> uint16_t nb_status, uint32_t >> *status) >> -- return value: the number of failed completed operations. >> And here I agree with Morten: we should design API which adapts to DPDK >> service scenarios. So we don't support some sound-cards DMA, and 2D >> memory >> copy which mainly used in video scenarios. > > Can I suggest a few adjustments here to the semantics of this API. In > future we may have operations which return a status value, e.g. our > hardware can support ops like compare equal/not-equal, which means that > this API would be meaningful even in case of success. Therefore, I suggest > that the return value be changed to allow success also to be returned in > the array, and the return value is not the number of failed ops, but the > number of ops for which status is being returned. > > Also for consideration: when trying to implement this in a prototype in our > driver, it would be easier if we relax the restriction on the "completed" > API so that we can flag has_error when an error is detected rather than > guaranteeing to return all elements right up to the error. For example, if > we have a burst of packets and one is problematic, it may be easier to flag > the error at the start of the burst and then have a few successful entries > at the start of the completed_status array. [Separate from this] We should > also have a "has_error" or "more_errors" flag on this API too, to indicate > when the user can switch back to using the regular "completed" API. This > means that apps switch from one API to the other when "has_error" is true, > and only switch back when it becomes false again. > We've discussed this before, and I prefer a relatively straightforward API, so in the new version I'll explicitly name it as rte_dmadev_completed_fails. We can continue this on the new patch, and I think that's probably the biggest difference.
