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. 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); >> --
