From: David Miller <davem@davemloft.net>
To: sri@us.ibm.com
Cc: shemminger@osdl.org, rdreier@cisco.com, netdev@vger.kernel.org
Subject: Re: Excess use of packed attribute
Date: Mon, 07 Aug 2006 17:39:20 -0700 (PDT) [thread overview]
Message-ID: <20060807.173920.102575221.davem@davemloft.net> (raw)
In-Reply-To: <1154995328.11916.24.camel@w-sridhar2.beaverton.ibm.com>
From: Sridhar Samudrala <sri@us.ibm.com>
Date: Mon, 07 Aug 2006 17:02:08 -0700
> All the structures in sctp.h that use packed atrribute define
> standard on-wire SCTP chunk/parameter formats. They need to be at the
> exact offsets as they go on wire.
> I think we saw some issues without the packed attribute on 64-bit archs
> and just to be safe we added packed to all the on-wire structures.
For the cases where it is no actually necessary, the code generation
cost on RISC cpus is very high. Byte loads and stores will be used to
access _every_ member of such structures on RISC machines because
the compiler cannot guarentee the alignment of any data object
when packed is specified.
It's OK to do this when it's really needed, but when it's not it
should be heavily avoided.
next prev parent reply other threads:[~2006-08-08 0:39 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-08-07 20:34 Excess use of packed attribute Stephen Hemminger
2006-08-07 23:20 ` David Miller
2006-08-09 19:17 ` Ville Nuorvala
2006-08-08 0:02 ` Sridhar Samudrala
2006-08-08 0:39 ` David Miller [this message]
2006-08-09 18:37 ` Roland Dreier
2006-08-10 4:11 ` David Miller
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