linux-kernel - Re: RFC: THE OFFLINE SCHEDULER

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Message-ID: <4A97DD88.5090504@hp.com>
Date:	Fri, 28 Aug 2009 09:37:12 -0400
From:	jim owens <jowens@...com>
To:	Rik van Riel <riel@...hat.com>
CC:	raz ben yehuda <raziebe@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Chris Friesen <cfriesen@...tel.com>,
	Andrew Morton <akpm@...ux-foundation.org>, mingo@...e.hu,
	peterz@...radead.org, maximlevitsky@...il.com, efault@....de,
	wiseman@...s.biu.ac.il, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.org
Subject: Re: RFC: THE OFFLINE SCHEDULER

Rik van Riel wrote:
> raz ben yehuda wrote:
> 
>> yes. latency is a crucial property. 
> 
> In the case of network packets, wouldn't you get a lower
> latency by transmitting the packet from the CPU that
> knows the packet should be transmitted, instead of sending
> an IPI to another CPU and waiting for that CPU to do the
> work?
> 
> Inter-CPU communication has always been the bottleneck
> when it comes to SMP performance.  Why does adding more
> inter-CPU communication make your system faster, instead
> of slower like one would expect?
> 

Maybe just me being paranoid, but from the beginning this
"use for dedicated IO processor" has scared the crap out of me.

Reminds me of Winmodem... sell cheap hardware by stealing your CPU!

The HPC FIFO user application on the other hand is a reasonable
if somewhat edge-case specialized user batch job.

jim
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