On 06/30, Maciej Fijalkowski wrote: > On Fri, Jun 27, 2025 at 04:57:44PM +0800, Jason Xing wrote: > > From: Jason Xing <kernelxing@xxxxxxxxxxx> > > > > For afxdp, the return value of sendto() syscall doesn't reflect how many > > descs handled in the kernel. One of use cases is that when user-space > > application tries to know the number of transmitted skbs and then decides > > if it continues to send, say, is it stopped due to max tx budget? > > > > The following formular can be used after sending to learn how many > > skbs/descs the kernel takes care of: > > > > tx_queue.consumers_before - tx_queue.consumers_after > > > > Prior to the current patch, in non-zc mode, the consumer of tx queue is > > not immediately updated at the end of each sendto syscall when error > > occurs, which leads to the consumer value out-of-dated from the perspective > > of user space. So this patch requires store operation to pass the cached > > value to the shared value to handle the problem. > > > > More than those explicit errors appearing in the while() loop in > > __xsk_generic_xmit(), there are a few possible error cases that might > > be neglected in the following call trace: > > __xsk_generic_xmit() > > xskq_cons_peek_desc() > > xskq_cons_read_desc() > > xskq_cons_is_valid_desc() > > It will also cause the premature exit in the while() loop even if not > > all the descs are consumed. > > > > Based on the above analysis, using @sent_frame could cover all the possible > > cases where it might lead to out-of-dated global state of consumer after > > finishing __xsk_generic_xmit(). > > > > The patch also adds a common helper __xsk_tx_release() to keep align > > with the zc mode usage in xsk_tx_release(). > > > > Signed-off-by: Jason Xing <kernelxing@xxxxxxxxxxx> > > Acked-by: Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx> Acked-by: Stanislav Fomichev <sdf@xxxxxxxxxxx>
