Date: Tue, 15 Mar 2005 11:43:10 -0600
To: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Hollis Blanchard <hollis@penguinppc.org>, akpm@osdl.org,
       linuxppc64-dev@ozlabs.org, torvalds@osdl.org,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] PPC64 iSeries: cleanup viopath
Message-ID: <20050315174310.GH498@austin.ibm.com>
References: <20050315143412.0c60690a.sfr@canb.auug.org.au> <0961a209ce72bb9f2a01b163aa6e6fbd@penguinppc.org> <20050316025339.318fc246.sfr@canb.auug.org.au>
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From: Linas Vepstas <linas@austin.ibm.com>
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On Wed, Mar 16, 2005 at 02:53:39AM +1100, Stephen Rothwell was heard to remark:
> On Tue, 15 Mar 2005 08:32:27 -0600 Hollis Blanchard <hollis@penguinppc.org> wrote:
> > 
> > Why not use a byte instead of a full int (reordering the members for 
> > alignment)?
> 
> Because "classical" boleans are ints.
> 
> Because I don't know the relative speed of accessing single byte variables.
> 
> Because it was easy.
> 
> Because we only allocate 32 of these structures.  Changing them really
> only adds four bytes per structure.  I guess using bytes and rearranging
> the structure could actually save 4 bytes per structure.

FWIW, keep in mind that a cache miss due to large structures not fitting
is a zillion times more expensive than byte-aligning in the cpu 
(even if byte operands had a cpu perf overhead, which I don't think 
they do on ppc).

> It really makes little difference, 

Yep. So my apologies for making you read this email.

--linas

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