linux-kernel - Re: [RESEND][PATCH v3 14/17] static_call: Add static_cond

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Message-ID: <20200324165454.GT20696@hirez.programming.kicks-ass.net>
Date:   Tue, 24 Mar 2020 17:54:54 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Jason Baron <jbaron@...mai.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Nadav Amit <namit@...are.com>,
        Peter Anvin <hpa@...or.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [RESEND][PATCH v3 14/17] static_call: Add static_cond_call()

On Tue, Mar 24, 2020 at 09:14:03AM -0700, Linus Torvalds wrote:
> On Tue, Mar 24, 2020 at 7:25 AM Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > Extend the static_call infrastructure to optimize the following common
> > pattern:
> >
> >         if (func_ptr)
> >                 func_ptr(args...)
> 
> Is there any reason why this shouldn't be the default static call pattern?
> 
> IOW, do we need the special "cond" versions at all? Couldn't we just
> say that this is how static calls fundamentally work - if the function
> is NULL, they are nops?

That doesn't work for functions that have a return value ...