linux-kernel - Re: [PATCH RFC 1/2] sched/core: Convert synchronize_rcu_mult to synchronize

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Message-ID: <20181002212019.GC89166@joelaf.mtv.corp.google.com>
Date:   Tue, 2 Oct 2018 14:20:19 -0700
From:   Joel Fernandes <joel@...lfernandes.org>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        Ingo Molnar <mingo@...hat.com>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH RFC 1/2] sched/core: Convert synchronize_rcu_mult to
 synchronize_rcu

On Mon, Oct 01, 2018 at 08:38:01PM -0700, Paul E. McKenney wrote:
> On Mon, Oct 01, 2018 at 06:20:11PM -0700, Joel Fernandes wrote:
> > From: "Joel Fernandes (Google)" <joel@...lfernandes.org>
> > 
> > synchronize_rcu_mult is now obsolete since all the different RCU flavors
> > have been consolidated and the API is now common on the updater side.
> > sched/core.c is the only user of it. All call_rcu_<flavor> calls boil
> > down to the same call_rcu. So there's no point in calling
> > synchronize_rcu_mult infact it could potentially be slower due to
> > waiting for the call_rcu callback twice. Just call synchronize_rcu here
> > which should do the job.
> > 
> > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> 
> Well, the theory was that I was going to keep this series hidden until
> the consolidation hit mainline just to avoid confusion, but please see
> 5fc9d4e000b1 ("rcu: Eliminate synchronize_rcu_mult()"), which I just
> now pushed to -rcu.  To your credit, you did get most of it.  ;-)

Glad you already took care of that ;-) I should have taken a peek at rcu/test
branch :D

> Here is the full list:
> 
> pick 1f3e6eaed8fa Apply coccinelle script to consolidate calls to RCU-bh and RCU-sched
> pick 5fc9d4e000b1 rcu: Eliminate synchronize_rcu_mult()
> pick a8475496801e rcu: Consolidate the RCU update functions invoked by sync.c
> pick d8ffb03461ad sched/membarrier: Replace synchronize_sched() with synchronize_rcu()
> 
> Of course, I will need to rerun the coccinelle script and split the
> result across subsystems, but I am waiting until the current pull
> request hits mainline.  Let's face it, none of us need to do debugging
> on someone consolidating their RCU updates before at least this commit
> and its predecessors hit mainline:
> 
> 709fdce7545c ("rcu: Express Tiny RCU updates in terms of RCU rather than RCU-sched")
> 
> I sent the pull request to Ingo a few days ago, so with some luck this
> will all get to mainline during the next merge window, and then it is
> open season on outside-of-RCU cleanups.  ;-)

Cool, thanks,

 - Joel