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    SubjectRe: prioritize PCI traffic ?

    Soeren Sonnenburg wrote:
    > On Mon, 2007-01-15 at 19:23 +0530, Vaidyanathan Srinivasan wrote:
    >> Soeren Sonnenburg wrote:
    >>> Dear all,
    >>> is it possible to explicitly tell the kernel to prioritize PCI traffic
    >>> for a number of cards in pci slots x,y,z ?
    >>> I am asking as severe ide traffic causes lost frames when watching TV
    >>> using 2 DVB cards + vdr... This is simply due to the fact that the PCI
    >>> bus is saturated...
    >> How do you know that the bus is saturated?
    > I simply dd if=/dev/sd? of=/dev/null from four brand new sata-harddisks.
    >> Are you streaming data to/from the ide hard disks/CDROM?
    > yes.
    >> Do you have DMAs 'ON' for the hard disks?
    > yes.


    >> Is everything just fine if there are no IDE traffic?
    > yes.


    >> Are you running 2.6 kernel with preempt 'ON'?

    Try CONFIG_PREEMPT=y it may help. It made the system more responsive
    for me.

    >> Are all hardware on the same IRQ line? (shared interrupts)
    > no: libata devices are on IRQ 16 and DVB devices on IRQ 20

    Watch the interrupt count (/proc/interrupts) and interrupt rate,
    that may give some clue on what is happening on the PCI bus.

    >>> So, is any prioritizing of the PCI bus possible ?
    >> The drivers + application indirectly can control priority on the
    >> bus. Just reduce the priority of the application that uses IDE and
    >> see if adjusting nice values of applications can change the scenario.
    > That unfortunately did not help... no change...

    33Mhz 32-bit PCI bus on typical PC can do around 100MB/sec... watch
    your individual disk transfer rates and data rate to each DVB.
    dd from 4 new SATA drive will probably fillup the bus. However,
    depending on your motherboard, the integrated SATA controllers may
    be on a different PCI bus than the one for the slots.

    You can watch the lspci output to determine which bus the devices
    are located.


    > Soeren
    > --
    > Sometimes, there's a moment as you're waking, when you become aware of
    > the real world around you, but you're still dreaming.
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