linux-kernel - Re: [cpuops cmpxchg double V2 1/4] Generic support for this_cpu_cmpxchg

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Message-ID: <ae2cc2e9-6516-4acf-bfad-5b6947ef11c4@email.android.com>
Date:	Sun, 23 Jan 2011 10:00:30 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Tejun Heo <tj@...nel.org>
CC:	Pekka Enberg <penberg@...helsinki.fi>,
	Christoph Lameter <cl@...ux.com>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [cpuops cmpxchg double V2 1/4] Generic support for	this_cpu_cmpxchg_double

Don't apply "packed" to a structure which needs padding!  That's just user error.

"Mathieu Desnoyers" <mathieu.desnoyers@...icios.com> wrote:

>* Tejun Heo (tj@...nel.org) wrote:
>[...]
>> > (note: packed here along with "aligned" does _not_ generate ugly
>> > bytewise read/write memory ops like "packed" alone. The use of
>> > "packed" is to let the compiler down-align the structure to the
>> > value requested, instead of uselessly aligning it on 32-byte if it
>> > chooses to.)
>> 
>> Yeah, good point.  :-)
>
>For the records, I just noticed that "packed, aligned(8)" can generate
>unaligned
>accesses on sparc64 by removing the padding between a "int" and a
>following
>pointer. So we should not use it.
>
>Thanks,
>
>Mathieu
>
>-- 
>Mathieu Desnoyers
>Operating System Efficiency R&D Consultant
>EfficiOS Inc.
>http://www.efficios.com

-- 
Sent from my mobile phone.  Please pardon any lack of formatting.
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