From: Bruce Richardson <bruce.richardson@intel.com>
To: "Morten Brørup" <mb@smartsharesystems.com>
Cc: dev@dpdk.org, Olivier Matz <olivier.matz@6wind.com>
Subject: Re: [dpdk-dev] Weird 2 KB MBUF data room requirement
Date: Fri, 10 Jul 2020 11:26:09 +0100 [thread overview]
Message-ID: <20200710102609.GA684@bricha3-MOBL.ger.corp.intel.com> (raw)
In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35C61113@smartserver.smartshare.dk>
On Fri, Jul 10, 2020 at 10:21:40AM +0200, Morten Brørup wrote:
> Dear Ethernet PMD developers,
>
> According to rte_mbuf_core.h, RTE_MBUF_DEFAULT_DATAROOM is 2048 bytes because some NICs need at least 2 KB buffer to receive standard Ethernet frames without splitting them into multiple segments.
>
> This is a serious waste of memory, considering that standard Ethernet frames are max 1518 bytes.
>
> How wide spread is this limitation... is it common or a rare exception?
>
> Where is it documented which NICs suffer from this limitation?
>
> Do any Intel NICs suffer from this limitation?
>
>
> NB: We are targeting an MBUF total size (incl. memzone element overhead) of 2^N, and this limitation would increase our MBUF total size to 4 KB.
>
>
> Med venlig hilsen / kind regards
> - Morten Brørup
>
AFAIK: the NICs supported by the ixgbe driver only allow the size to be
specified in KB granularity.
However, it may be safe to have a driver modification whereby anything over
1600 bytes is considered as 2KB if jumbo frame support is disabled. I don't
think anyone has actually looked into doing so though, or if there are
other hidden gotchas about attempting to do so.
/Bruce
next prev parent reply other threads:[~2020-07-10 10:26 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-10 8:21 Morten Brørup
2020-07-10 10:26 ` Bruce Richardson [this message]
2020-07-10 12:58 ` Olivier Matz
2020-07-10 13:45 ` Morten Brørup
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