On Mon Jan 20, 2025 at 10:56 AM CET, Alexandra Winter wrote: > > > On 20.01.25 07:32, Dust Li wrote: > >> + /** > >> + * move_data() - write into a remote dmb > >> + * @dev: Local sending ism device > >> + * @dmb_tok: Token of the remote dmb > >> + * @idx: signalling index > >> + * @sf: signalling flag; > >> + * if true, idx will be turned on at target ism interrupt mask > >> + * and target device will be signalled, if required. > >> + * @offset: offset within target dmb > >> + * @data: pointer to data to be sent > >> + * @size: length of data to be sent > >> + * > >> + * Use dev to write data of size at offset into a remote dmb > >> + * identified by dmb_tok. Data is moved synchronously, *data can > >> + * be freed when this function returns. > > When considering the API, I found this comment may be incorrect. > > > > IIUC, in copy mode for PCI ISM devices, the CPU only tells the > > device to perform a DMA copy. As a result, when this function returns, > > the device may not have completed the DMA copy. > > > > No, it is actually one of the properties of ISM vPCI that the data is > moved synchronously inside the move_data() function. (on PCI layer the > data is moved inside the __zpci_store_block() command). > Obviously for loopback move_data() is also synchornous. That is true for the IBM ISM vPCI device but maybe we should design the API also for future PCI devices that do not move data synchronously. > > SMC-D does not make use of it, instead they re-use the same > conn->sndbuf_desc for the lifetime of a connection. > > > > In zero-copy mode for loopback, the source and destination share the > > same buffer. If the source rewrites the buffer, the destination may > > encounter corrupted data. The source should only reuse the data after > > the destination has finished reading it. > > > > That is true independent of the question, whether the move is > synchronous or not. > It is the clients' responsibility to make sure a sender does not > overwrite unread data. SMC uses the write-pointers and read-pointer for > that. > > > > Best regards, > > Dust > > > >> + * > >> + * If signalling flag (sf) is true, bit number idx bit will be > >> + * turned on in the ism signalling mask, that belongs to the > >> + * target dmb, and handle_irq() of the ism client that owns this > >> + * dmb will be called, if required. The target device may chose to > >> + * coalesce multiple signalling triggers. > >> + */ > >> int (*move_data)(struct ism_dev *dev, u64 dmb_tok, unsigned int idx, > >> bool sf, unsigned int offset, void *data, > >> unsigned int size); > >> --
