linux-kernel - Re: [RFC PATCH 4/8] preempt: Introduce CONFIG_PREEMPT

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Date:   Thu, 28 Jan 2021 13:17:53 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...nel.org>, Mel Gorman <mgorman@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Michal Hocko <mhocko@...e.com>,
        ardb@...nel.org, jpoimboe@...hat.com
Subject: Re: [RFC PATCH 4/8] preempt: Introduce CONFIG_PREEMPT_DYNAMIC

On Fri, Jan 22, 2021 at 05:53:43PM +0100, Peter Zijlstra wrote:
> On Mon, Jan 18, 2021 at 03:12:19PM +0100, Frederic Weisbecker wrote:
> > +config HAVE_PREEMPT_DYNAMIC
> > +	bool
> > +	depends on HAVE_STATIC_CALL_INLINE
> 
> I think we can relax this to HAVE_STATIC_CALL, using trampolines
> shouldn't be too bad, and that would put it in reach of arm64.

Why not, but then I need to make CONFIG_PREEMPT_DYNAMIC optional
in order not to make the overhead mandatory for everyone.

> 
> > +	depends on GENERIC_ENTRY
> > +	help
> > +	   Select this if the architecture support boot time preempt setting
> > +	   on top of static calls. It is strongly advised to support inline
> > +	   static call to avoid any overhead.