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SubjectRe: 2.5.69 Interrupt Latency
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On Mon, 2003-05-12 at 08:57, Paul Fulghum wrote:
> On Fri, 2003-05-09 at 16:28, Andrew Morton wrote:
>
> > This code was added to wakeup_hc(). It is called from uhci_irq():
> >
> > + /* Global resume for 20ms */
> > + outw(USBCMD_FGR | USBCMD_EGSM, io_addr + USBCMD);
> > + wait_ms(20);
> >
> > The changelog just says "Minor patch for uhci-hcd.c"
> >
> > Can you delete the wait_ms() and see if that is our culprit?
>
> This is the culprit.
>
> Removing this line corrects the latency problems on
> the server. A 20ms delay seems pretty excessive for an
> interrupt handler. I'm not sure what it is supposed to
> accomplish, but this seems like something that should
> be scheduled to run outside of the ISR.
>
> I must have messed up a test on the laptop that is
> also showing latency problems. On the laptop the
> problem *is* in both 2.5.68/2.5.69 and *is not*
> eliminated by turning off USB. The laptop uses the
> ohci driver anyways which is not effected by this patch.
> The laptop does not show latency problems on 2.4.20.
>
> So the patch above is definately a problem,
> but the problem I am seeing on the laptop
> is something unrelated, but part of 2.5.x
> (which I will investigate further).
>
> Thanks,
> Paul

I forgot to add this snippet from the /var/log/messages file
of the server in case it helps the USB maintainer
in evaluating what to do about the above patch.

kernel: drivers/usb/host/uhci-hcd.c: USB Universal Host Controller Interface driver v2.0
kernel: uhci-hcd 00:04.2: Intel Corp. 82371AB/EB/MB PIIX4
kernel: uhci-hcd 00:04.2: irq 19, io base 0000fce0
kernel: Please use the 'usbfs' filetype instead, the 'usbdevfs' name is deprecated.
kernel: uhci-hcd 00:04.2: new USB bus registered, assigned bus number 1
kernel: hub 1-0:0: USB hub found
kernel: hub 1-0:0: 2 ports detected

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


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