linux-kernel - Re: taskstats alignment...

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Message-ID: <20101224211529.GA19019@bicker>
Date:	Sat, 25 Dec 2010 00:16:39 +0300
From:	Dan Carpenter <error27@...il.com>
To:	Jeff Mahoney <jeffm@...e.com>
Cc:	David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org,
	balbir@...ux.vnet.ibm.com,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: taskstats alignment...

On Fri, Dec 24, 2010 at 01:45:29PM -0500, Jeff Mahoney wrote:
v> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> On 12/23/2010 12:30 PM, David Miller wrote:
> > 
> > Re: commit 4be2c95d1f7706ca0e74499f2bd118e1cee19669
> > 
> > Pretty much every 64-bit architecture other than
> > powerpc64 and x86-64 needs that code, not just
> > IA64.
> > 
> > Better check would be:
> > 
> > CONFIG_64BIT && !CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
> > 
> > Otherwise we'll be twiddling that ifdef endlessly as each
> > and every other 64-bit platform bumps into this issue.
> > 
> > So please could you change this to use a more sane check?
> 
> I don't have an objection to it, but I've been pushing that we make the
> change universal from the beginning of the discussion.
> 
> The issue is that it causes breakage on apps that aren't following the
> interface properly. iotop, in particular, has hard-coded offsets into
> the packet to fish out the taskstats structure.
> 
> So, if the goal of not breaking x86_64 is good enough, I'm fine with
> this change.

Didn't you say something along the lines that if they don't have
CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS then there is a warning message
printed in dmesg?  I thought that was what prompted you to change the
alignment in the first place.  It sound like those arches are already
broken so David's suggestion would be a clear improvement over the 
current code.

BTW, since you're redoing the patch, it would be good if you pasted the
warning message into the changelog.

regards,
dan carpenter

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