From: Jeff Garzik <jeff@garzik.org>
To: "Kok, Auke" <auke-jan.h.kok@intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>,
Ayyappan Veeraiyan <ayyappan.veeraiyan@intel.com>,
netdev@vger.kernel.org, akpm@linux-foundation.org
Subject: Re: [PATCH] ixgbe: Introduce new 10GbE driver for Intel 82598 based PCI Express adapters...
Date: Mon, 02 Jul 2007 11:32:41 -0400 [thread overview]
Message-ID: <46891A99.7090003@garzik.org> (raw)
In-Reply-To: <46891939.2030805@intel.com>
Kok, Auke wrote:
> Maybe this is not most important for ixgbe, where we only have 8 or so
> flags, but the new e1000 driver that I posted this weekend currently has
> 63 (you wanted flags ;)) of them. Do you want me to use 63 integers or
> just 2 ?
Don't be silly. We are talking about single-bit feature flags
implemented using machine ints (a la tg3 with 32 flags per int), versus
bitfields.
Bitfields are to be avoided for many reasons:
* more difficult, in general, for a compiler to generate optimal code
* in particular, known to generate worse code on various architectures
* often causes endian problems
* often enhances programmer confusion, when trying to review structs and
determine optimal layout and alignment
* programmers have proven they will screw up bitfields in e.g. cases
with 1-bit and signedness.
I can probably think up more reasons to avoid bitfields if given another
5 minutes :)
Jeff
next prev parent reply other threads:[~2007-07-02 15:32 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-06-12 23:44 [ANNOUNCE] new driver ixgbe for Intel(R) 10GbE PCI Express adapters Ayyappan.Veeraiyan
2007-06-12 23:44 ` [PATCH] ixgbe: Introduce new 10GbE driver for Intel 82598 based " Ayyappan Veeraiyan
2007-07-02 12:52 ` Jeff Garzik
2007-07-02 14:05 ` Arjan van de Ven
2007-07-02 14:25 ` Jeff Garzik
2007-07-02 14:27 ` Arjan van de Ven
2007-07-02 14:41 ` Jeff Garzik
2007-07-02 14:41 ` Arjan van de Ven
2007-07-02 15:26 ` Kok, Auke
2007-07-02 15:32 ` Jeff Garzik [this message]
2007-07-02 15:52 ` Andrew Morton
2007-07-02 16:09 ` Jeff Garzik
2007-07-02 15:54 ` Kok, Auke
2007-07-06 8:46 ` Ingo Oeser
2007-07-02 14:31 ` Arjan van de Ven
2007-07-02 19:00 ` Veeraiyan, Ayyappan
2007-07-02 19:04 ` Ayyappan Veeraiyan
2007-07-02 20:16 ` Christoph Hellwig
2007-07-02 21:09 ` Stephen Hemminger
2007-07-02 21:42 ` Christoph Hellwig
2007-07-02 22:02 ` Kok, Auke
2007-07-02 22:08 ` Jeff Garzik
2007-07-02 22:10 ` Michael Buesch
2007-07-02 22:16 ` Jeff Garzik
2007-07-02 23:57 ` Kok, Auke
2007-07-03 0:11 ` Jeff Garzik
2007-07-03 0:16 ` Inaky Perez-Gonzalez
2007-07-03 13:19 ` Jeff Garzik
2007-07-03 18:24 ` Inaky Perez-Gonzalez
2007-07-05 23:29 ` Jeff Garzik
2007-07-03 0:08 ` Veeraiyan, Ayyappan
2007-07-03 22:01 ` Ayyappan Veeraiyan
2007-07-02 22:56 ` Veeraiyan, Ayyappan
2007-07-03 12:53 ` Neil Horman
2007-07-05 12:37 ` Neil Horman
2007-07-09 14:21 ` Veeraiyan, Ayyappan
2007-07-10 0:57 ` Neil Horman
2007-06-13 23:05 ` [ANNOUNCE] new driver ixgbe for Intel(R) 10GbE " Francois Romieu
2007-06-13 23:18 ` Kok, Auke
2007-06-14 0:06 ` Ayyappan Veeraiyan
2007-06-14 20:36 ` Francois Romieu
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