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    SubjectRe: [PATCH] SLUB use cmpxchg_local
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    On Tue, 2007-08-28 at 12:36 -0700, Christoph Lameter wrote:
    > On Tue, 28 Aug 2007, Peter Zijlstra wrote:
    >
    > > On Mon, 2007-08-27 at 15:15 -0700, Christoph Lameter wrote:
    > > > Hmmmm. One wild idea would be to use a priority futex for the slab lock?
    > > > That would make the slow paths interrupt safe without requiring interrupt
    > > > disable? Does a futex fit into the page struct?
    > >
    > > Very much puzzled at what you propose. in-kernel we use rt_mutex (has
    > > PI) or mutex, futexes are user-space. (on -rt spinlock_t == mutex ==
    > > rt_mutex)
    > >
    > > Neither disable interrupts since they are sleeping locks.
    > >
    > > That said, on -rt we do not need to disable interrupts in the allocators
    > > because its a bug to call an allocator from raw irq context.
    >
    > Right so if a prioriuty futex

    futex stands for Fast Userspace muTEX, please lets call it a rt_mutex.

    > would have been taken from a process
    > context and then an interrupt thread (or so no idea about RT) is scheduled
    > then the interrupt thread could switch to the process context and complete
    > the work there before doing the "interrupt" work. So disabling interrupts
    > is no longer necessary.

    -rt does all of the irq handler in thread (process) context, the hard
    irq handler just does something akin to a wakeup.

    These irq threads typically run fifo/50 or simething like that.

    [ note that this allows a form of irq priorisation even if the hardware
    doesn't. ]

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