From: John Bradford <john@grabjohn.com>
To: jamesclv@us.ibm.com
Cc: lunz@falooley.org, linux-kernel@vger.kernel.org
Subject: Re: detecting hyperthreading in linux 2.4.19
Date: Thu, 9 Jan 2003 21:54:05 +0000 (GMT) [thread overview]
Message-ID: <200301092154.h09Ls5SX005123@darkstar.example.net> (raw)
In-Reply-To: <200301091337.04957.jamesclv@us.ibm.com> from "James Cleverdon" at Jan 09, 2003 01:37:04 PM
> > Is there a way for a userspace program running on linux 2.4.19 to tell
> > the difference between a single hyperthreaded xeon P4 with HT enabled
> > and a dual hyperthreaded xeon P4 with HT disabled? The /proc/cpuinfos
> > for the two cases are indistinguishable.
>
> I don't know of any way to do this in userland. The whole point is that the
> sibling processors are supposed to look like real ones.
>
> You _could_ try running two processes simultaneously in tight spin loops for
> 100 million cycles and comparing the amount of real time consumed. That
> would be rather unreliable and kludgey though.
If /proc/interrupts shows a processor is handling interrupts then it
is definitely a 'real' one. If it isn't handling interrupts, it may
or may not be a 'real' one. That's another unreliable and kludgey way
to tell the difference :-).
John.
next prev parent reply other threads:[~2003-01-09 21:46 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-01-09 20:02 detecting hyperthreading in linux 2.4.19 Jason Lunz
2003-01-09 21:37 ` James Cleverdon
2003-01-09 21:54 ` John Bradford [this message]
2003-01-10 0:16 ` James Cleverdon
2003-01-10 0:58 ` Mike Dresser
2003-01-09 21:57 ` Jason Lunz
2003-01-10 12:29 ` Mark Hounschell
2003-01-10 7:05 ` Mikael Pettersson
2003-01-10 11:05 ` Dave Jones
2003-01-10 11:19 ` Mikael Pettersson
2003-01-10 0:20 ` Dave Jones
-- strict thread matches above, loose matches on Subject: below --
2003-01-09 22:29 Kamble, Nitin A
2003-01-09 23:26 Pallipadi, Venkatesh
2003-01-10 8:16 Pallipadi, Venkatesh
2003-01-10 8:43 ` Mikael Pettersson
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