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    SubjectRe: 2.5.69 Interrupt Latency
    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,
    Microgate Corporation,

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