linux-kernel - Re: [PATCH 1/4] [x86] Add command line option to enable/disable hyper-threading.

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Date:	Thu, 30 Nov 2006 11:06:11 +0000
From:	Alan <alan@...rguk.ukuu.org.uk>
To:	Ben Collins <bcollins@...ntu.com>
Cc:	linux-kernel@...r.kernel.org, torvalds@...l.org
Subject: Re: [PATCH 1/4] [x86] Add command line option to enable/disable
 hyper-threading.

On Wed, 29 Nov 2006 23:26:05 -0500
Ben Collins <bcollins@...ntu.com> wrote:

> This patch adds a config option to allow disabling hyper-threading by
> default, and a kernel command line option to changes this default at
> boot time.
> 
> Signed-off-by: Ben Collins <bcollins@...ntu.com>

The description is wrong - this does not disable hyperthreading it merely
leaves one thread idle. I don't believe Intel have ever published a
procedure for truely disabling HT, but if you idle a thread you may want
to adjust the cache settings on a PIV (10.5.6 in the intel docs) and set
it to shared mode. Need to play more with what the bios does I guess.

So Ack but with the proviso it should say "Ignoring" or "Not using" not
"Disabling", because it does not do the latter and there seem to be
performance differences as a result

Acked-by: Alan Cox <alan@...hat.com>

Alan
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