Re[5]: Modem + Network in Xircom cards, and maybe others

From: Carlos Velasco (freebsd_at_newipnet.com)
Date: 05/17/04

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    Date: Mon, 17 May 2004 13:30:45 +0200
To: "Bruce Evans" <bde@zeta.org.au>

    On 06/05/2004 at 16:44 Bruce Evans wrote:

    >On Wed, 5 May 2004, Carlos Velasco wrote:
    >
    >> On 06/05/2004 at 0:26 Bruce Evans wrote:
    >>
    >> >However, you may need only this part of it. This part permits software
    >> >interrupts to be delayed by 38 ticks instead of the expected maximim
    >> >of 2 ticks. I keep forgetting to fix this. Scaling by hz is not quite

    Yes, this patch in sio.c seems to work perfectly. So I think sio swi is
    being delayed somewhere by Giant or any other thing.

    >> >right, because hz may be set to values that are too small to work all
    >> >the time or even most of the time. There is a clamp to 128 (min), but
    >> >this is a bit small. E.g., with hz = 1000 and speed = 115200, the
    >> >original code in the above gives cp4ticks = 44 and ibufsize = 128. If

    what about if we fix the value or making it adjustable via sysctl?

    >The broken interrupt priorities are easy to see in "ps laxw | sort -n +4"
    >output. Note that the highest priorities are numerically lowest:
    > 0 27 0 0 -48 0 0 12 - WL ?? 0:00.06 (swi8:
    >tty:cy+ clock)
    >
    > [I think this is supposed to be the low priority softclock ithread
    > (the "slow" cy and sio SWIs attach to it and misname themselves as
    > tty:cy and tty:sio instead of clk:cy and clk:sio). It actually has
    > _highest_ priority among SWIs, so the problem is sort of the opposite
    > of what I thought, but mostly worse. The "slow" cy and sio SWIs
    > actually have the same bogus high priority, so they don't compete
    > with other SWIs. However, they compete with softclock, and all
    > other SWIs have lower priority than softclock so they don't even
    > compete with it. This is the reverse of what is supposed to
    > happen. I think softclock starts with the correct low priority, but
    > its priority gets clobbered when the cy and sio SWIs attach to it.
    >
    > 0 37 0 0 -48 0 0 12 - WL ?? 0:00.00 (swi0:
    >tty:cy+)
    >
    > [I think this is the "fast" cy and sio SWI. Verbose names which get
    > truncated complicate debugging.]

    I have here:

        0 22 0 0 -80 0 0 12 - WL ?? 0:00.01 (irq11:
    cbb0 cbb1+)
    ...
        0 28 0 0 -48 0 0 12 - WL ?? 0:01.74 (swi8:
    tty:sio clock)
        0 39 0 0 -48 0 0 12 - WL ?? 0:00.00 (swi0:
    tty:sio)

    So, I assume you are right.

    >> I believe this patch to sio.c is only a temporary solution that should
    be
    >> removed when GIANT dissapears in most drivers, am I right?
    >
    >No, it (the cp4ticks one) is a more general patch, though it is temporary
    >because it is not in its final form. Best-case interrupt latency cannot
    >be guaranteed for SWIs, and even a saftey margin of a factor of 4 is not
    >enough even without the Giant and priority bugs, since it doesn't scale
    >right when "hz" is configured to large values, and configuring "hz" to
    >too-large values is now encouraged by DEVICE_POLLING.

    Could we commit it or something similar?
    I think sio is normal mode is broken for high speeds cause this like my
    problem with modem pccard.

    Regards,
    Carlos Velasco

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