linux-kernel - Re: [PATCH 1/2] srcu: Fix broken node geometry after early ssp init

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Message-ID: <20210419002345.GA161053@lothringen>
Date:   Mon, 19 Apr 2021 02:23:45 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Josh Triplett <josh@...htriplett.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH 1/2] srcu: Fix broken node geometry after early ssp init

On Sat, Apr 17, 2021 at 09:46:16PM -0700, Paul E. McKenney wrote:
> On Sat, Apr 17, 2021 at 03:16:49PM +0200, Frederic Weisbecker wrote:
> > On Wed, Apr 14, 2021 at 08:55:38AM -0700, Paul E. McKenney wrote:
> > > > diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
> > > > index 75ed367d5b60..24db97cbf76b 100644
> > > > --- a/kernel/rcu/rcu.h
> > > > +++ b/kernel/rcu/rcu.h
> > > > @@ -278,6 +278,7 @@ extern void resched_cpu(int cpu);
> > > >  extern int rcu_num_lvls;
> > > >  extern int num_rcu_lvl[];
> > > >  extern int rcu_num_nodes;
> > > > +extern bool rcu_geometry_initialized;
> > > 
> > > Can this be a static local variable inside rcu_init_geometry()?
> > > 
> > > After all, init_srcu_struct() isn't called all that often, and its overhead
> > > is such that an extra function call and check is going to hurt it.  This
> > > of course requires removing __init from rcu_init_geometry(), but it is not
> > > all that large, so why not just remove the __init?
> > > 
> > > But if we really are worried about reclaiming rcu_init_geometry()'s
> > > instructions (maybe we are?), then rcu_init_geometry() can be split
> > > into a function that just does the check (which is not __init) and the
> > > remainder of the function, which could remain __init.
> > 
> > There you go:
> 
> Queued, thank you!

Thanks!

And please also consider "[PATCH 2/2] srcu: Early test SRCU polling start"
if you want to expand testing coverage to polling.