<div dir="ltr">Hi Ferruh,<div> </div><div>In my case, the traffic is not large, so I can't see the impact. I also tested under high load(>2Mpps with 2 DPDK cores and 2 kernel threads) and found no significant difference in performance either. I think the reason should be that it will not run to 'kni_fifo_count(kni->alloc_q) == 0' under high load. </div></div> <div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Jan 3, 2023 at 8:47 PM Ferruh Yigit <<a href="mailto:ferruh.yigit@amd.com">ferruh.yigit@amd.com</a>> wrote: </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">On 12/30/2022 4:23 AM, Yangchao Zhou wrote: > In some scenarios, mbufs returned by rte_kni_rx_burst are not freed > immediately. So kni_allocate_mbufs may be failed, but we don't know. > > Even worse, when alloc_q is completely exhausted, kni_net_tx in > rte_kni.ko will drop all tx packets. kni_allocate_mbufs is never > called again, even if the mbufs are eventually freed. > > In this patch, we try to allocate mbufs for alloc_q when it is empty. > > According to historical experience, the performance bottleneck of KNI > is offen the usleep_range of kni thread in rte_kni.ko. > The check of kni_fifo_count is trivial and the cost should be acceptable. > Hi Yangchao, Are you observing any performance impact with this change in you use case? > Fixes: 3e12a98fe397 ("kni: optimize Rx burst") > Cc: <a href="mailto:stable@dpdk.org" target="_blank">stable@dpdk.org</a> > > Signed-off-by: Yangchao Zhou <<a href="mailto:zhouyates@gmail.com" target="_blank">zhouyates@gmail.com</a>> > --- > lib/kni/rte_kni.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/lib/kni/rte_kni.c b/lib/kni/rte_kni.c > index 8ab6c47153..bfa6a001ff 100644 > --- a/lib/kni/rte_kni.c > +++ b/lib/kni/rte_kni.c > @@ -634,8 +634,8 @@ rte_kni_rx_burst(struct rte_kni *kni, struct rte_mbuf **mbufs, unsigned int num) > { > unsigned int ret = kni_fifo_get(kni->tx_q, (void **)mbufs, num); > > - /* If buffers removed, allocate mbufs and then put them into alloc_q */ > - if (ret) > + /* If buffers removed or alloc_q is empty, allocate mbufs and then put them into alloc_q */ > + if (ret || (kni_fifo_count(kni->alloc_q) == 0)) > kni_allocate_mbufs(kni); > > return ret; </blockquote></div>