linux-kernel - Re: [PATCH v2 tip/core/rcu 08/18] rcu: Remove short-term CPU kicking

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Date:   Mon, 23 Jan 2017 11:36:30 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Josh Triplett <josh@...htriplett.org>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
        fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH v2 tip/core/rcu 08/18] rcu: Remove short-term CPU kicking

On Sat, Jan 21, 2017 at 12:43:44PM -0800, Josh Triplett wrote:
> On Tue, Jan 17, 2017 at 06:53:47PM -0800, Paul E. McKenney wrote:
> > Commit 4914950aaa12d ("rcu: Stop treating in-kernel CPU-bound workloads
> 
> Does this commit ID still match what you have in your tree, post-rebase?

In light of your earlier email, good question!  But this one is still
OK because it is already in mainline.

							Thanx, Paul

> > as errors") added a (relatively) short-timeout call to resched_cpu().
> > This was inspired by as issue that was fixed by b7e7ade34e61 ("sched/core:
> > Fix remote wakeups").  But given that this issue was fixed, it is time
> > for the current commit to remove this call to resched_cpu().
> > 
> > Reported-by: Byungchul Park <byungchul.park@....com>
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > Reviewed-by: Josh Triplett <josh@...htriplett.org>
> > ---
> >  kernel/rcu/tree.c | 5 -----
> >  1 file changed, 5 deletions(-)
> > 
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 0e61b62e3f4a..5a4aaad75e76 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -1220,11 +1220,6 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
> >  		rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */
> >  	}
> >  
> > -	/* And if it has been a really long time, kick the CPU as well. */
> > -	if (ULONG_CMP_GE(jiffies,
> > -			 rdp->rsp->gp_start + 2 * jiffies_till_sched_qs) ||
> > -	    ULONG_CMP_GE(jiffies, rdp->rsp->gp_start + jiffies_till_sched_qs))
> > -		resched_cpu(rdp->cpu);  /* Force CPU into scheduler. */
> >  	/*
> >  	 * If more than halfway to RCU CPU stall-warning time, do
> >  	 * a resched_cpu() to try to loosen things up a bit.
> > -- 
> > 2.5.2
> > 
>