On Tue, Jul 19, 2016 at 10:52:08AM +0200, Christoph Hellwig wrote:
>
> On Mon, Jul 18, 2016 at 03:37:46PM +1000, Dave Chinner wrote:
> > > The reason I did this in the first place was a vague notion that
> > > unconditional
> > > packing was harmful.
> > >
> > > http://digitalvampire.org/blog/index.php/2006/07/31/why-you-shouldnt-use-__attribute__packed/
> > >
> > > "However, it's actively harmful to add the attribute to a structure that's
> > > already going to be laid out with no padding."
> > > ...
> > > "gcc gets scared about unaligned accesses and generates six times as much
> > > code
> > > (96 bytes vs. 16 bytes)! sparc64 goes similarly crazy, bloating from 12
> > > bytes
> > > to 52 bytes"
> > >
> > > I don't know if that's (still) correct or not, but that was the reason
> > > for the selective __pack application way back when. Might be worth
> > > investigating?
> >
> > Christoph? The first two ptches are fine, but more info is needed
> > for this one...
>
> I don't have a sparc64 compiler to test unfortunately. But I can confirm
> that on x86-64 xfs.o is bit to bit identical with or without the patch.
OK, that's probably good enough to go with for now. Thanks for
following up, Christoph.
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
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