Re: [RFC PATCH 5/6] implement per-cpu&per-domain state machine call_srcu()

[Peter Zijlstra <peterz@infradead.org>]

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.