On 8/9/2018 11:23 AM, Kiran Kumar wrote: > With existing code in kni_fifo_put, rx_q values are not being updated > before updating fifo_write. While reading rx_q in kni_net_rx_normal, > This is causing the sync issue on other core. So adding a write > barrier to make sure the values being synced before updating fifo_write. > > Fixes: 3fc5ca2f6352 ("kni: initial import") > > Signed-off-by: Kiran Kumar <kkokkilaga...@caviumnetworks.com> > --- > lib/librte_kni/rte_kni_fifo.h | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/lib/librte_kni/rte_kni_fifo.h b/lib/librte_kni/rte_kni_fifo.h > index ac26a8c..4d6b33e 100644 > --- a/lib/librte_kni/rte_kni_fifo.h > +++ b/lib/librte_kni/rte_kni_fifo.h > @@ -39,6 +39,7 @@ kni_fifo_put(struct rte_kni_fifo *fifo, void **data, > unsigned num) > fifo->buffer[fifo_write] = data[i]; > fifo_write = new_write; > } > + rte_smp_wmb(); > fifo->write = fifo_write; > return i;
For Intel this is just a compiler barrier so no issue but not sure if a memory barrier is required here, Related code block is: |- for (i = 0; i < num; i++) { || new_write = (new_write + 1) & (fifo->len - 1); || || if (new_write == fifo_read) || break; || fifo->buffer[fifo_write] = data[i]; || fifo_write = new_write; || } | fifo->write = fifo_write; "fifo_write" is updated in the loop, so there is a dependency to it for "fifo->write". Can memory writes be reordered when there is a dependency? Cc'ed a few more people for comment.