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    SubjectRe: [PATCH] block: strip out locking optimization in put_io_context()
    On Wed, Feb 08, 2012 at 08:56:11AM -0800, Tejun Heo wrote:
    > On Wed, Feb 08, 2012 at 08:49:20AM -0800, Tejun Heo wrote:
    > > I'm still a bit lost on where the regression is coming from and
    > > *suspecting* that queue_lock contention is making the reverse locking
    > > behave much worse than expected, so I mostly wanted to take that out
    > > and see what happens.
    > IOW, we can achieve about the same thing by adding another lock in
    > request_queue. The goal is using an inner lock for ioc clearing so
    > that queue_lock doesn't have to be grabbed inside ioc lock.

    Urgh....... forget about the above message. My head is still booting.
    We can't do this w/ per-queue lock as we don't have a way to traverse
    the associated queues w/o holding the lock and we need read locking on
    ioc exit path as we may recurse through elevator icq exit (it's not
    about concurrency). /me goes to brew coffee.


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