netdev - Re: [PATCH] SIW: iWARP Protocol headers

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Message-ID: <OFC70D3F8A.C5D69C2F-ONC12577B4.0044CFB7-C12577B4.0046C012@ch.ibm.com>
Date:	Wed, 6 Oct 2010 14:52:46 +0200
From:	Bernard Metzler <BMT@...ich.ibm.com>
To:	Bart Van Assche <bvanassche@....org>
Cc:	linux-rdma@...r.kernel.org, linux-rdma-owner@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] SIW: iWARP Protocol headers



linux-rdma-owner@...r.kernel.org wrote on 10/05/2010 06:10:45 PM:

> On Tue, Oct 5, 2010 at 8:53 AM, Bernard Metzler <bmt@...ich.ibm.com>
wrote:
> > +} __attribute__((__packed__));
>
> Apparently you make extensive use of the packed attribute. Please read
> this blog entry, in which it is explained why this is harmful:
>
> http://digitalvampire.org/blog/index.php/2006/07/31/why-you-
> shouldnt-use-__attribute__packed/
>
right, thanks, i was not aware of that
big overhead.
but...there are reasons why we may need it _packed_:
(1) to get the size of the packet hdr
(2) to read/write the hdr content

(1) is not harmful. (2) could be limited to
just one read/write operation per rx/tx path
and all other access could be done on a
structure which contains the host representation
of the hdr content. both structures could coexist
in a union, part of the rx or tx context.
would that satisfy your complain?

many thanks,
bernard.


> Bart.
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