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    SubjectRe: [PATCH] fix PHY polling system blocking
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    I had now analyzed the PHY handling in most of the network drivers. Most
    of the PHY communication will be handled in a polling/blocking way,
    write a command word and then wait for the results. Due the nature of
    the PHY attachment, this will take some time.

    Some of the network drivers do this polling/blocking also in atomic code
    paths, like interrupts or timer. So activities on the PHY can cause huge
    latency jitters.

    On the other side, most of the network driver handle the PHY without
    using or only partially using the phylib.

    The phylib has also a drawback, because it polls the PHY despite if it
    has interrupt support for it or not. I can't see a reason for this
    behavior.

    So the problem of huge latencies by polling the PHY occurs in most of
    the network drivers. For example have a look at the e100 network driver
    in the file drivers/net/e100.c, function mdio_ctrl_hw(): This function
    will poll for max. of 4000 us or 4 ms.

    To fix this latency jitter problem with the PHY polling there are the
    following steps to do:

    - disable polling in driver/net/phy.c if an interrupt for the PHY is
    available
    - create an own single or per cpu workqueue for the phylib, so that the
    PHY specific code can temporary schedule or block
    - prevent all current user of the phylib to access the PHY in a atomic
    code path
    - modify all current users of the phylib from using cpu_relax() to
    cond_resched() and replace the counters against inquiring a timeout
    - modify all other network drivers to use the phylib

    What do you think?

    Stefani




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