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    SubjectRe: [RFC][PATCH 2/6] lockdep: validate rcu_dereference() vs rcu_read_lock()
    On 9/19/07, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
    > On Wed, 19 Sep 2007 16:41:04 -0400 "Dmitry Torokhov"
    > <dmitry.torokhov@gmail.com> wrote:
    >
    > > > If the IRQ handler does rcu_read_lock(),unlock() and the i8042_stop()
    > > > function does sync_rcu() instead of _sched(), it should be good again.
    > > > It will not affect anything else than the task that calls _stop(). And
    > > > even there the only change is that the sleep might be a tad longer.
    > >
    > > And the IRQ handler needs to do some extra job... Anyway, it looks -rt
    > > breaks synchronize_sched() and needs to have it fixed:
    > >
    > > "/**
    > > * synchronize_sched - block until all CPUs have exited any non-preemptive
    > > * kernel code sequences.
    > > *
    > > * This means that all preempt_disable code sequences, including NMI and
    > > * hardware-interrupt handlers, in progress on entry will have completed
    > > * before this primitive returns."
    >
    > That still does as it says in -rt. Its just that the interrupt handler
    > will be preemptible so the guarantees it gives are useless.

    Please note "... including NMI and hardware-interrupt handlers ..."

    >
    > > > I find it curious that a driver that is 'low performant' and does not
    > > > suffer lock contention pioneers locking schemes. I agree with
    > > > optimizing, but this is not the place to push the envelope.
    > >
    > > Please realize that evey microsecond wasted on a 'low performant'
    > > driver is taken from high performers and if we can help it why
    > > shouldn't we?
    >
    > sure, but the cache eviction caused by running the driver will have
    > more impact than the added rcu_read_{,un}lock() calls.

    Are you saying that adding rcu_read_{,un}lock() will help with cache
    eviction? How?

    --
    Dmitry
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