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From: Ferruh Yigit <ferruh.yigit@amd.com>
To: Matt <zhouyates@gmail.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 14:34:16 +0000	[thread overview]
Message-ID: <e7c17c4c-f6fe-3442-17f8-b682ff797b47@amd.com> (raw)
In-Reply-To: <CABLiTuyutdYGGMDA+hvcoKScZRL6M1+qQxJLiwGwHnFp8=g4Lw@mail.gmail.com>

On 1/4/2023 11:57 AM, Matt wrote:
> 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.
> 

I agree, additional check most likely hit on the low bandwidth,
thanks for checking for performance impact.

> On Tue, Jan 3, 2023 at 8:47 PM Ferruh Yigit <ferruh.yigit@amd.com
> <mailto: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 <mailto:stable@dpdk.org>
>     >
>     > Signed-off-by: Yangchao Zhou <zhouyates@gmail.com
>     <mailto:zhouyates@gmail.com>>

Acked-by: Ferruh Yigit <ferruh.yigit@amd.com>


  reply	other threads:[~2023-01-04 14:34 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
2023-01-04 14:34         ` Ferruh Yigit [this message]
2023-03-11  9:16           ` Thomas Monjalon

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