[RC5] hyper threading on Intel P4

Jeff Lawson jlawson at bovine.net
Fri Dec 20 12:49:33 EST 2002


Some comments regarding this are in this bug report:
http://n0cgi.distributed.net/bugs/show_bug.cgi?id=2790


On Thu, 19 Dec 2002, Adam Crews wrote:

> Hello,
>
> It appears that the new P4 3.06 ghz chip with intel's hyper threading performs much much slower when 2 rc5 threads are started.  This chip presents it's self as 2 cpu's to the OS, and as a result dnet automatically starts 2 threads.  The client version is dnetc v2.9001-477-CTR-02111118 for Win32 (WindowsNT 5.1).
>
> When this happens, the machine cracks a horid 2 million keys a second.
> [Dec 19 05:36:48 UTC] 2 crunchers ('a' and 'b') have been started.
> --snip--
> [Dec 19 15:25:07 UTC] RC5-72: Summary: 18 packets (18.00 stats units)
>                       0.09:51:44.17 - [2,117,507 keys/s]
>
>
> When the client is configured to only start 1 thread, it runs much better at 4 million keys a second:
> [Dec 20 05:05:05 UTC] 1 cruncher has been started.
> [Dec 20 05:17:04 UTC] RC5-72: Completed CA:4263E76E:00000000 (1.00 stats units)
>                       0.00:11:59.10 - [4,214,779 keys/s]
>
> It appears that the threads are steping on each other and generally slowing things down.
>
> If the guys working on the x86 cores would like to test code on this chip, I am willing to give it a run and provide any feedback.
>
> Or if anyone has any ideas on why this happens this way, I would be interested to know.
>
> -Adam
>
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-- 
Jeff Lawson   http://www.bovine.net/  http://www.distributed.net/~bovine/
Jeffrey_Lawson at alumni.hmc.edu  jlawson at bovine.net  bovine at distributed.net
Programmer, Developer, Mascot, Founder of the largest computer on earth!
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