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    SubjectRe: [PATCH 2/3] work_on_cpu: Use our own workqueue.
    On Tue, 10 Feb 2009 19:24:07 +1030 Rusty Russell <rusty@rustcorp.com.au> wrote:

    > On Thursday 05 February 2009 02:06:36 Andrew Morton wrote:
    > > On Wed, 4 Feb 2009 21:11:35 +1030 Rusty Russell <rusty@rustcorp.com.au> wrote:
    > >
    > > > On Wednesday 04 February 2009 13:31:11 Andrew Morton wrote:
    > > > > On Wed, 4 Feb 2009 13:14:31 +1030 Rusty Russell <rusty@rustcorp.com.au> wrote:
    > > > > > I think you're right though: smp_call_function_single (or neat wrappers)
    > > > > > where possible, work_on_cpu which can fail for the others, and we'll just
    > > > > > have to plumb in the error returns.
    > > > >
    > > > > I bet a lot of those can use plain old schedule_work_on().
    > > >
    > > > Which is where work_on_cpu started: a little wrapper around schedule_work_on.
    > > >
    > > > We're going in circles, no?
    > >
    > > No, we've made some progress. We have a better understanding of what
    > > the restrictions, shortcomings and traps are in this stuff. We've
    > > learned (surprise!) that a one-size-fits-all big hammer wasn't such a
    > > great idea.
    > >
    > > Proposed schedule_work_on() rule: either the flush_work() caller or the
    > > callback should not hold any explicit or implicit sleeping locks.
    >
    > But as you found out looking through these, it's really hard to tell. I can
    > guess, but that's a little fraught...

    yup.

    > How about we make work_on_cpu spawn a temp thread; if you care, use
    > something cleverer? Spawning a thread just isn't that slow.

    That's what
    work_on_cpu-rewrite-it-to-create-a-kernel-thread-on-demand.patch does?

    > Meanwhile, I'll prepare patches to convert all the non-controversial cases
    > (ie. smp_call_function-style ones).

    arch-x86-kernel-acpi-cstatec-avoid-using-work_on_cpu.patch
    arch-x86-kernel-cpu-cpufreq-acpi-cpufreqc-avoid-using-work_on_cpu.patch
    arch-x86-kernel-cpu-mcheck-mce_amd_64c-avoid-using-work_on_cpu.patch

    convert three work_on_cpu() callers. The drivers/pci/pci-driver.c one
    is a bit problematic.

    I guess as long as we don't find a high frequency set_cpus_allowed()
    callsite which can't be converted to smp_call_function_single() we'll
    be OK.


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