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From: Matt Laswell <laswell@infiniteio.com>
To: Alex Markuze <alex@weka.io>
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] segmented recv ixgbevf
Date: Wed, 5 Nov 2014 08:48:50 -0600
Message-ID: <CA+GnqApDx88-vXQeid20wJgV2iER6dTD2XWARzrAaCY09WTCgg@mail.gmail.com> (raw)
In-Reply-To: <CAKfHP0Vq5ExWpEBRtehJ7_SUBhbbTP8sfEDHyc164yAjMijZOw@mail.gmail.com>

Hey Folks,

I ran into the same issue that Alex is describing here, and I wanted to
expand just a little bit on his comments, as the documentation isn't very
clear.

Per the documentation, the two arguments to rte_pktmbuf_pool_init() are a
pointer to the memory pool that contains the newly-allocated mbufs and an
opaque pointer.  The docs are pretty vague about what the opaque pointer
should point to or what it's contents mean; all of the examples I looked at
just pass a NULL pointer. The docs for this function describe the opaque
pointer this way:

"A pointer that can be used by the user to retrieve useful information for
mbuf initialization. This pointer comes from the init_arg parameter of
rte_mempool_create()
<http://www.dpdk.org/doc/api/rte__mempool_8h.html#a7dc1d01a45144e3203c36d1800cb8f17>
."

This is a little bit misleading.  Under the covers, rte_pktmbuf_pool_init()
doesn't threat the opaque pointer as a pointer at all.  Rather, it just
converts it to a uint16_t which contains the desired mbuf size.   If it
receives 0 (in other words, if you passed in a NULL pointer), it will use
2048 bytes + RTE_PKTMBUF_HEADROOM.  Hence, incoming jumbo frames will be
segmented into 2K chunks.

Any chance we could get an improvement to the documentation about this
parameter?  It seems as though the opaque pointer isn't a pointer and
probably shouldn't be opaque.

Hope this helps the next person who comes across this behavior.

--
Matt Laswell
infinite io, inc.

On Thu, Oct 30, 2014 at 7:48 AM, Alex Markuze <alex@weka.io> wrote:

> For posterity.
>
> 1.When using MTU larger then 2K its advised to provide the value
> to rte_pktmbuf_pool_init.
> 2.ixgbevf rounds down the ("MBUF size" - RTE_PKTMBUF_HEADROOM) to the
> nearest 1K multiple when deciding on the receiving capabilities [buffer
> size]of the Buffers in the pool.
> The function SRRCTL register,  is considered here for some reason?
>

      parent reply	other threads:[~2014-11-05 14:39 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-10-30 10:23 Alex Markuze
2014-10-30 11:09 ` Bruce Richardson
2014-10-30 12:48   ` Alex Markuze
2014-10-30 13:18     ` Bruce Richardson
2014-11-05 14:48     ` Matt Laswell [this message]

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