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SubjectRE: 2.6.11, USB: High latency?
Date
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> * kus Kusche Klaus <kus@keba.com> wrote:
> > IRQ 7-724 0d..1 1us : end_8259A_irq (do_hardirq)
> > IRQ 7-724 0d..1 1us!: enable_8259A_irq (do_hardirq)
> > IRQ 7-724 0d... 832us : do_hardirq (do_irqd)
> > IRQ 7-724 0d... 833us : trace_irqs_on (do_hardirq)
>
> > mmap-1000 0d.h1 21us : end_8259A_irq (__do_IRQ)
> > mmap-1000 0d.h1 22us!: enable_8259A_irq (__do_IRQ)
> > mmap-1000 0d.h. 662us : irq_exit (do_IRQ)
> > mmap-1000 0d..1 662us : do_softirq (irq_exit)
>
> > mmap-1000 0d.h. 0us : do_IRQ (c012d6d5 7 0)
> > mmap-1000 0d.h1 2us!: mask_and_ack_8259A (__do_IRQ)
> > mmap-1000 0d.h1 938us : redirect_hardirq (__do_IRQ)
> > mmap-1000 0d.h1 939us : wake_up_process (redirect_hardirq)
>
> such 'freezes' almost certainly signal some sort of hardware
> latency -
> some device holding the system bus up during DMA. There is no
> algorithmic reason for any of those steps above to take
> several hundreds
> of microseconds.
>
> Ingo

I asked our hardware team. The hardware has two devices which are
in use and capable of busmaster/DMA transfers:
The intel e100 ethernet controller and the intel PIIX4 USB
controller.
The IDE interface is also a busmaster, but there are only PIO IDE
devices.

I suspect the latter, as USB reads were running in parallel...
How many bytes are transferred at most by the USB controller
for a single request? How long may this take?

Any experiences / opinitions / advices?

Moreover, we know from experience that the "WBINDV" instruction
(Write back and invalidate CPU cache) can cause such latencies.

Does this instruction occur anywhere in Linux?

--
Klaus Kusche (Software Development - Control Systems)
KEBA AG Gewerbepark Urfahr, A-4041 Linz, Austria (Europe)
Tel: +43 / 732 / 7090-3120 Fax: +43 / 732 / 7090-8919
E-Mail: kus@keba.com WWW: www.keba.com
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