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    SubjectRe: [PATCH v3 3/4] irq: Allow multiple clients to register for irq affinity notification
    Hi Thomas,

    On Fri, Oct 17 2014 at 01:29 -0600, Thomas Gleixner wrote:
    >On Fri, 10 Oct 2014, Lina Iyer wrote:
    >> On Wed, Oct 08 2014 at 09:03 -0600, Thomas Gleixner wrote:
    >> > On Thu, 25 Sep 2014, Lina Iyer wrote:
    >> > > > How would a general "keep track of the targets of all interrupts in
    >> > > > the system" mechanism make use of this?
    >> > > Sorry, I do not understand your question.
    >> > > PM QoS is only interested in the IRQs specified in the QoS request. If
    >> > > there are no requests that need to be associated with an IRQ, then PM
    >> > > QoS will not register for an affinity change notification.
    >> >
    >> > Right, and I really hate the whole per irq notifier. It's a rats nest
    >> > of life time issues and other problems.
    >> >
    >> > It also does not tell you whether an irq is disabled, reenabled or
    >> > removed, which will change the qos constraints as well unless you
    >> > plaster all drivers with updates to qos for those cases.
    >> >
    >> > So what about adding a qos field to irq_data itself, have a function
    >> > to update it and let the irq core keep track of the per cpu irq
    >> > relevant qos constraints and provide an evaluation function or a
    >> > notifier for the PM/idle code?
    >>
    >> If that isnt intrusive in the IRQ core, then we can make it work for PM
    >> QoS. The issue that I am concerned is that, it might result in back and
    >> forth between IRQ and PM QoS frameworks. If that doesnt happen, then we
    >> are good with this approach.
    >
    >I can't tell that upfront, but I think it's worth to explore it.
    >
    I was able to review the options and I attempted a few methods, but
    off-loading the QoS onto the IRQ framework, made it quite complex to
    manage it. QoS values for each of the four constraints and the
    constraints could be one of 3 types - min, max or sum, makes it a whole
    lot of mess handling it in IRQ code.

    I was able to get QoS to be notified of IRQ affinity changes without
    using notifiers, but, I still am yet to find a way to modify QoS
    requests on enable/disable of IRQ.

    I will send the RFC of the new patchset, would be interested in taking a
    look and let me know what you think.

    Thanks,
    Lina


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