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From: Matt <zhouyates@gmail.com>
To: Ferruh Yigit <ferruh.yigit@amd.com>
Cc: dev@dpdk.org, stephen@networkplumber.org, stable@dpdk.org
Subject: Re: [PATCH v3] kni: fix possible alloc_q starvation when mbufs are exhausted
Date: Wed, 4 Jan 2023 19:57:29 +0800	[thread overview]
Message-ID: <CABLiTuyutdYGGMDA+hvcoKScZRL6M1+qQxJLiwGwHnFp8=g4Lw@mail.gmail.com> (raw)
In-Reply-To: <042de5cd-c410-7925-efe9-bea547fec736@amd.com>

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Hi Ferruh,

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.

On Tue, Jan 3, 2023 at 8:47 PM Ferruh Yigit <ferruh.yigit@amd.com> wrote:

> 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: stable@dpdk.org
> >
> > Signed-off-by: Yangchao Zhou <zhouyates@gmail.com>
> > ---
> >  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;
>
>

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  reply	other threads:[~2023-01-04 11:57 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-09  5:13 [PATCH] " Yangchao Zhou
2022-11-09  6:04 ` [PATCH v2] " Yangchao Zhou
2022-11-09 16:39   ` Stephen Hemminger
2022-11-11  9:12     ` Matt
2022-12-09 16:15       ` Ferruh Yigit
2022-12-30  4:23   ` [PATCH v3] " Yangchao Zhou
2023-01-03 12:47     ` Ferruh Yigit
2023-01-04 11:57       ` Matt [this message]
2023-01-04 14:34         ` Ferruh Yigit
2023-03-11  9:16           ` Thomas Monjalon

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