linux-kernel - Re: [patch V6 12/37] x86/entry: Provide idtentry_entry/exit_cond

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Message-ID: <20200521133920.GY2869@paulmck-ThinkPad-P72>
Date:   Thu, 21 May 2020 06:39:20 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Jason Chen CJ <jason.cj.chen@...el.com>,
        Zhao Yakui <yakui.zhao@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch V6 12/37] x86/entry: Provide
 idtentry_entry/exit_cond_rcu()

On Thu, May 21, 2020 at 10:31:11AM +0200, Thomas Gleixner wrote:
> "Paul E. McKenney" <paulmck@...nel.org> writes:
> > On Wed, May 20, 2020 at 03:15:31PM -0700, Paul E. McKenney wrote:
> > Same patch, but with updated commit log based on IRC discussion
> > with Andy.
> 
> Fun. I came up with the same thing before going to bed. Just that I
> named the function differently: rcu_irq_enter_check_tick()

I am good with that name.

> >  #if defined(CONFIG_TINY_RCU)
> >  
> > +static inline void tickle_nohz_for_rcu(void)
> > +{
> > +}
> > +
> >  static inline void rcu_nmi_enter(void)
> >  {
> >  }
> > @@ -23,6 +27,7 @@ static inline void rcu_nmi_exit(void)
> >  }
> >  
> >  #else
> > +extern void tickle_nohz_for_rcu(void);
> 
> And I made this a NOP for for !NOHZ_FULL systems and avoided the call if
> context tracking is not enabled at boot.
> 
> void __rcu_irq_enter_check_tick(void);
> 
> static inline void rcu_irq_enter_check_tick(void)
> {
> 	if (context_tracking_enabled())
>         	__rcu_irq_enter_check_tick();
> }

That certainly is a better approach!

So let's go with your version.  But could you please post it, just in
case reviewing an alternative version causes me to spot something?

							Thanx, Paul