[Beowulf] cluster softwares supporting parallel CFD computing

Vincent Diepeveen diep at xs4all.nl
Fri Sep 8 18:36:26 EDT 2006


----- Original Message ----- 
From: "Eric W. Biederman" <ebiederm at xmission.com>
To: "Ashley Pittman" <ashley at quadrics.com>
Cc: "'Bogdan Costescu'" <Bogdan.Costescu at iwr.uni-heidelberg.de>; "'Beowulf 
List'" <beowulf at beowulf.org>; "Daniel Kidger" 
<daniel.kidger at clearspeed.com>; "'Mark Hahn'" <hahn at physics.mcmaster.ca>
Sent: Thursday, September 07, 2006 7:54 PM
Subject: Re: [Beowulf] cluster softwares supporting parallel CFD computing


> Ashley Pittman <ashley at quadrics.com> writes:
>
>> I think Daniel was talking about supercomputer networks and not
>> ethernet, on the first QsNet2 machine I have to hand latency without
>> interrupts is 2.72uSec, using interrupts it is 7.20uSec.  One
>> fundamental difference between these two measurements is that when you
>> use interrupts the kernel has to get involved, without interrupts it
>> doesn't so you don't just have the interrupt but also a extra syscall.
>>
>> I know of people who have tried to tune the Hz rate down as low as 10,
>> I'm fairly sure they wrote a paper about it.
>
> Ok.  Those numbers sound believable.  Although they feel a little high,
> which probably just means no one has done any serious tuning there.
>
> At 5us latency after polling for just a short while you can likely
> go to sleep without experiencing any real penalty.  Say within a 
> milisecond
> or so of polling you can sleep.
>
> Eric

How about the latency to wake up that thread again. runqueue latency in 
linux is 10+ ms?

Vincent
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