From: Samuel Flory <sflory@rackable.com>
To: Mark Mielke <mark@mark.mielke.cc>
Cc: mcuss@cdlsystems.com, jamesclv@us.ibm.com,
root@chaos.analogic.com, linux-kernel@vger.kernel.org
Subject: Re: Kernel reports 4 CPUS instead of 2...
Date: Wed, 16 Oct 2002 15:14:24 -0700 [thread overview]
Message-ID: <3DADE4C0.9030809@rackable.com> (raw)
In-Reply-To: 20021016214455.GA9624@mark.mielke.cc
Mark Mielke wrote:
>On Wed, Oct 16, 2002 at 01:47:32PM -0700, Samuel Flory wrote:
>
>
>> Try shutting off hyperthreading in the bios. Keep in mind
>>hyperthreading is net loss if you are running a single nonthreaded app.
>>Also you might want to check if there aren't io speed issues.
>>
>>
>
>Is this true? It seems to me that the 'on-demand execution units' would
>simply be devoted to the one task, resulting in zero loss.
>
>
In perfect world yes, but in reality there is overhead. I've tested
this on a quad xeon. A "make bzImage" is a bit faster with
hyperthreading off. Of course a make -j 8 bzImage is faster with
hyperthreading on. I haven't tried this on a dual xeon. (It could be a
scaling issue 4 vs 8 processors.)
>I see hyperthreading becoming a problem if two threads are scheduled to
>execute at the same time before the operating system, and if they each
>need access to the same execution units at the same time.
>
>
And if both threads need different items in L(whatever) cache it gets
even worse.
There are a few good overviews on the subject:
http://www.intel.com/technology/hyperthread/
http://arstechnica.com/paedia/h/hyperthreading/hyperthreading-1.html
http://www.anandtech.com/cpu/showdoc.html?i=1576&p=2
next prev parent reply other threads:[~2002-10-16 22:01 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-10-16 17:24 Kernel reports 4 CPUS instead of 2 Mark Cuss
2002-10-16 17:35 ` Richard B. Johnson
2002-10-16 17:56 ` Samuel Flory
2002-10-16 17:54 ` Richard B. Johnson
2002-10-16 18:14 ` Samuel Flory
2002-10-16 19:28 ` James Cleverdon
2002-10-16 19:44 ` Mark Cuss
2002-10-16 20:10 ` Richard B. Johnson
2002-10-16 20:47 ` Samuel Flory
2002-10-16 21:44 ` Mark Mielke
2002-10-16 22:14 ` Samuel Flory [this message]
2002-10-16 22:21 ` Mark Cuss
2002-10-16 18:37 ` Mark Cuss
2002-10-16 23:21 ` Bryan Whitehead
2002-10-17 0:34 ` Mark Chernault
2002-10-17 12:56 ` Richard B. Johnson
2002-10-17 14:19 ` Dave Jones
2002-10-17 17:15 ` Bryan B Whitehead
2002-10-16 17:37 ` Joel Jaeggli
2002-10-16 17:48 ` Mark Cuss
2002-10-16 17:44 ` FD Cami
-- strict thread matches above, loose matches on Subject: below --
2002-10-16 18:08 Nakajima, Jun
2002-10-17 1:02 Matt_Domsch
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