linux-kernel - Re: TREE_SRCU slows hotplug by factor ~16

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Message-ID: <1493271840.4154.25.camel@gmx.de>
Date:   Thu, 27 Apr 2017 07:44:00 +0200
From:   Mike Galbraith <efault@....de>
To:     paulmck@...ux.vnet.ibm.com
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: TREE_SRCU slows hotplug by factor ~16

On Wed, 2017-04-26 at 22:32 -0700, Paul E. McKenney wrote:
> On Thu, Apr 27, 2017 at 06:15:56AM +0200, Mike Galbraith wrote:
> > On Wed, 2017-04-26 at 21:11 -0700, Paul E. McKenney wrote:
> > 
> > > This is with srcutree.exp_holdoff set to 25*1000?
> > 
> > Yup.
> 
> And please see below for the trivial patch, just for confirmation.
> May I add your Tested-by?

Sure.

> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index ccbe1fb84165..65f03bca5b32 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -39,7 +39,7 @@
>  
>  #include "rcu.h"
>  
> -ulong exp_holdoff = 50 * 1000; /* Holdoff (ns) for auto-expediting. */
> +ulong exp_holdoff = 25 * 1000; /* Holdoff (ns) for auto-expediting. */

Yup, exactly what I did.