linux-kernel - Re: [PATCH v6 15/17] static

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Message-ID: <20200711050831.GY597537@hirez.programming.kicks-ass.net>
Date:   Sat, 11 Jul 2020 07:08:31 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, mhiramat@...nel.org,
        bristot@...hat.com, jbaron@...mai.com,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        mingo@...nel.org, namit@...are.com, hpa@...or.com, luto@...nel.org,
        ard.biesheuvel@...aro.org, jpoimboe@...hat.com,
        pbonzini@...hat.com, mathieu.desnoyers@...icios.com,
        linux@...musvillemoes.dk
Subject: Re: [PATCH v6 15/17] static_call: Allow early init

On Fri, Jul 10, 2020 at 09:14:26PM -0400, Steven Rostedt wrote:
> On Fri, 10 Jul 2020 15:38:46 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > In order to use static_call() to wire up x86_pmu, we need to
> > initialize earlier; copy some of the tricks from jump_label to enable
> > this.
> > 
> > Primarily we overload key->next to store a sites pointer when there
> > are no modules, this avoids having to use kmalloc() to initialize the
> > sites and allows us to run much earlier.
> > 
> 
> I'm confused. What was the need to have key->next store site pointers
> in order to move it up earlier?

The critical part was to not need an allocation.