[Beowulf] cluster softwares supporting parallel CFD computing

Greg Lindahl greg.lindahl at qlogic.com
Thu Sep 7 04:46:56 EDT 2006


On Wed, Sep 06, 2006 at 11:10:14AM -0600, Eric W. Biederman wrote:

> There is fundamentally more work to do when you take an interrupt because
> you need to take a context switch.  But cost of a context switch is in
> the order of microseconds, so while measurable taking an interrupt should 
> not dramatically your latency numbers.

Unless, of course, your latency is a microsecond. In fact, our
*overhead* for a single message is much less than 1 usec, so an
interrupt per message would kill our message rate. And, finally, all
the cpus can poll main memory in an embarrassingly parallel fashion,
whereas interrupts involve OS contention.

> This is important as polling for new packets has a very significant opportunity
> cost as it prevents you from get any other work done at the same time

In most codes, the opportunity cost of polling is zero. But I can only
speak from my experience, do you have any data which shows different?

-- greg
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