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    SubjectRe: [RFC PATCH 5/6] implement per-cpu&per-domain state machine call_srcu()
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    On Fri, Mar 9, 2012 at 3:58 AM, Paul E. McKenney
    <paulmck@linux.vnet.ibm.com> wrote:
    > On Tue, Mar 06, 2012 at 04:34:53PM +0100, Peter Zijlstra wrote:
    >> On Tue, 2012-03-06 at 23:12 +0800, Lai Jiangshan wrote:
    >> > On Tue, Mar 6, 2012 at 7:16 PM, Peter Zijlstra <peterz@infradead.org> wrote:
    >> > > On Tue, 2012-03-06 at 17:57 +0800, Lai Jiangshan wrote:
    >> > >>         srcu_head is bigger, it is worth, it provides more ability and simplify
    >> > >>         the srcu code.
    >> > >
    >> > > Dubious claim.. memory footprint of various data structures is deemed
    >> > > important. rcu_head is 16 bytes, srcu_head is 32 bytes. I think it would
    >> > > be real nice not to have two different callback structures and not grow
    >> > > them as large.
    >> >
    >> > CC: tj@kernel.org
    >> > It could be better if workqueue also supports 2*sizeof(long) work callbacks.
    >>
    >> That's going to be very painful if at all possible.
    >>
    >> > I prefer ability/functionality a little more, it eases the caller's pain.
    >> > preemptible callbacks also eases the pressure of the whole system.
    >> > But I'm also ok if we limit the srcu-callbacks in softirq.
    >>
    >> You don't have to use softirq, you could run a complete list from a
    >> single worklet. Just keep the single linked rcu_head list and enqueue a
    >> static (per-cpu) worker to process the entire list.
    >
    > I like the idea of SRCU using rcu_head.  I am a little concerned about
    > what happens when there are lots of SRCU callbacks, but am willing to
    > wait to solve those problems until the situation arises.
    >
    > But I guess I should ask...  Peter, what do you expect the maximum
    > call_srcu() rate to be in your use cases?  If tens of thousands are
    > possible, some adjustments will be needed.

    Different from RCU(global domain), SRCU is separated
    by domains, I think the rate is not high for a given domain,
    but the real answer depends on the practice.

    >
    >                                                        Thanx, Paul
    >
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