linux-kernel - Re: Query regarding synchronize_sched_expedited and resched

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Message-ID: <20170921114640.6c9920a5@gandalf.local.home>
Date:   Thu, 21 Sep 2017 11:46:40 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Neeraj Upadhyay <neeraju@...eaurora.org>,
        paulmck@...ux.vnet.ibm.com, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        linux-kernel@...r.kernel.org, sramana@...eaurora.org,
        prsood@...eaurora.org, pkondeti@...eaurora.org,
        markivx@...eaurora.org
Subject: Re: Query regarding synchronize_sched_expedited and resched_cpu

On Thu, 21 Sep 2017 15:55:46 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Mon, Sep 18, 2017 at 11:11:05AM -0400, Steven Rostedt wrote:
> > On Sun, 17 Sep 2017 11:37:06 +0530
> > Neeraj Upadhyay <neeraju@...eaurora.org> wrote:
> >   
> > > Hi Paul, how about replacing raw_spin_trylock_irqsave with
> > > raw_spin_lock_irqsave in resched_cpu()? Are there any paths
> > > in RCU code, which depend on trylock check/spinlock recursion?  
> > 
> > It looks to me that resched_cpu() was added for nohz full sched
> > balancing, but is not longer used by that. The only user is currently
> > RCU. Perhaps we should change that from a trylock to a lock.  
> 
> No, regular NOHZ balancing. NOHZ FULL wasn't conceived back then.
> 
>   46cb4b7c88fa ("sched: dynticks idle load balancing")

Bah, every time I type NOHZ today I add FULL after it. I did mean NOHZ
without FULL. :-p

-- Steve