From: Tudor Cornea <tudor.cornea.keysight@gmail.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: Tudor Cornea <tudor.cornea@gmail.com>,
ferruh.yigit@intel.com, thomas@monjalon.net, dev@dpdk.org
Subject: Re: [PATCH] kernel/kni: retry the xmit in case ring is full
Date: Mon, 17 Jan 2022 17:29:55 +0200 [thread overview]
Message-ID: <CADFbcKdFndvKYji5gYe=JR96Y9LtWTVM7McORoLDjg+Yc_UN+w@mail.gmail.com> (raw)
In-Reply-To: <20211217082439.13d36631@hermes.local>
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Hi Stephen,
> NAK
> Doing this risks having a CPU lockup if userspace does not keep up
> or the DPDK application gets stuck.
>
> There are better ways to solve the TCP stack queue overrun issue:
> 1. Use a better queueing discipline on the kni device. The Linux default
> of pfifo_fast has bufferbloat issues. Use fq_codel, fq, codel or pie?
> 2. KNI should implement BQL so that TCP stack can see lock backpressure
> about possible queue depth.
>
>
Thanks for the suggestions.
I agree that we risk a lockup, in case the DPDK app gets stuck.
Indeed, I am running on an older Linux kernel, and the default queuing
discipline is pfifo_fast.
I'll experiment with the queuing disciplines you recommended.
> As a simple workaround increase the KNI ring size. It won't solve the whole
> problem but i tcan help
>
I obtained moderate success with increasing MAX_MBUF_BURST_NUM from 32 to
1024 in librte_kni.
I'm not sure if such a change would be upstreamable. Perhaps it needs a bit
of testing.
I'll drop the current patch.
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prev parent reply other threads:[~2022-01-17 15:30 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-17 15:00 Tudor Cornea
2021-12-17 16:24 ` Stephen Hemminger
2022-01-17 15:29 ` Tudor Cornea [this message]
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