Messages in this thread | | | Date | Thu, 8 Mar 2012 11:58:25 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [RFC PATCH 5/6] implement per-cpu&per-domain state machine call_srcu() |
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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.
Thanx, Paul
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