From: Linas Vepstas <linas@austin.ibm.com>
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
Date: Tue, 15 Mar 2005 11:43:10 -0600 [thread overview]
Message-ID: <20050315174310.GH498@austin.ibm.com> (raw)
In-Reply-To: <20050316025339.318fc246.sfr@canb.auug.org.au>
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
next prev parent reply other threads:[~2005-03-15 17:46 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-03-15 3:34 [PATCH] PPC64 iSeries: cleanup viopath Stephen Rothwell
2005-03-15 14:32 ` Hollis Blanchard
2005-03-15 15:53 ` Stephen Rothwell
2005-03-15 17:43 ` Linas Vepstas [this message]
2005-03-15 17:49 ` Brad Boyer
2005-03-16 15:12 ` Hollis Blanchard
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