Subject: Re: 2.5.69 Interrupt Latency
From: Paul Fulghum <paulkf@microgate.com>
To: Andrew Morton <akpm@digeo.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Fri, 2003-05-09 at 16:28, Andrew Morton wrote:
> Paul Fulghum <paulkf@microgate.com> wrote:
> >
> > In the process of eliminating kernel options to isolate
> > the problem, eliminating USB completely appears to fix it.
> > 
> > One machine (server) was using usb-uhci and
> > the other (laptop) was using usb-ohci.
> > 
> > So it looks like something with USB in 2.5.68-bk11

The latency problem seen on the laptop turned out to
be a stupid mistake on my part: I enabled the ALI15XX
IDE controller option as a module instead of in kernel
and so it was not available for using DMA mode. Once
corrected the latency is running at a smooth 20us without
the >5ms spikes associated with PIO IDE.

Final Diagnosis:

server latency problem = USB wakeup_hc() delay added in 2.5.68-bk11
laptop latency problem = user with dain bramage

Thanks,
Paul

-- 
Paul Fulghum, paulkf@microgate.com
Microgate Corporation, http://www.microgate.com


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