From: Stephen Hemminger <shemminger@linux-foundation.org>
To: "Jörn Engel" <joern@logfs.org>
Cc: Arnd Bergmann <arnd@arndb.de>,
virtualization@lists.linux-foundation.org,
Greg Kroah-Hartman <gregkh@suse.de>,
linux-kernel@vger.kernel.org, devel@driverdev.osuosl.org,
virtualization@lists.osdl.org, Sam Ramji <sramji@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Hank Janssen <hjanssen@microsoft.com>
Subject: Re: [patch 34/54] Staging: hv: remove STRUCT_PACKED and STRUCT_ALIGNED defines
Date: Fri, 24 Jul 2009 14:50:25 -0700 [thread overview]
Message-ID: <20090724145025.12da5a6e@nehalam> (raw)
In-Reply-To: <20090724213218.GA13702@logfs.org>
On Fri, 24 Jul 2009 23:32:19 +0200
Jörn Engel <joern@logfs.org> wrote:
> On Tue, 21 July 2009 01:46:41 +0200, Arnd Bergmann wrote:
> > On Friday 17 July 2009, Greg Kroah-Hartman wrote:
> > > @@ -43,7 +43,7 @@ typedef struct _RING_BUFFER {
> > > // volatile u32 InterruptMask;
> > > // Ring data starts here + RingDataStartOffset !!! DO NOT place any fields below this !!!
> > > u8 Buffer[0];
> > > -} STRUCT_PACKED RING_BUFFER;
> > > +} __attribute__((packed)) RING_BUFFER;
> > >
> >
> > The data structure is actually packed already, the attribute does not make it better
> > and could be removed. We also have __packed as a shortcut for __attribute__((packed)).
>
> Honestly, I don't know how useful __packed really is. In a shared
> kernel/userspace header, it is only defined for the kernel.
>
As I remember, gcc generates worse code for packed structures on many architectures
since it may have to do byte fetchs/recombining to avoid unaligned
accesses.
--
next prev parent reply other threads:[~2009-07-24 21:52 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20090717180850.873962925@mini.kroah.org>
[not found] ` <20090717180923.620590305@mini.kroah.org>
2009-07-20 23:39 ` [patch 47/54] Staging: hv: make gVmbusConnection.ChannelLock a real spinlock Arnd Bergmann
2009-07-21 2:11 ` Greg KH
[not found] ` <20090717180921.448023599@mini.kroah.org>
2009-07-20 23:46 ` [patch 34/54] Staging: hv: remove STRUCT_PACKED and STRUCT_ALIGNED defines Arnd Bergmann
2009-07-24 21:32 ` Jörn Engel
2009-07-24 21:50 ` Stephen Hemminger [this message]
2009-07-24 23:06 ` Jörn Engel
[not found] ` <20090717180920.285605541@mini.kroah.org>
2009-07-21 0:00 ` [patch 27/54] Staging: hv: remove ULONG and LONG typedefs Arnd Bergmann
2009-07-21 0:44 ` Hank Janssen
2009-07-21 2:38 ` Greg KH
2009-07-21 2:45 ` Greg KH
2009-07-21 8:26 ` Bernd Petrovitsch
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