linux-kernel - Re: [PATCH v6 06/17] static_call: Add basic static call infrastructure

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Date:   Fri, 10 Jul 2020 17:56:02 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.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 06/17] static_call: Add basic static call
 infrastructure

On Fri, 10 Jul 2020 15:38:37 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> From: Josh Poimboeuf <jpoimboe@...hat.com>
> 
> Static calls are a replacement for global function pointers.  They use
> code patching to allow direct calls to be used instead of indirect
> calls.  They give the flexibility of function pointers, but with
> improved performance.  This is especially important for cases where
> retpolines would otherwise be used, as retpolines can significantly
> impact performance.
> 
> The concept and code are an extension of previous work done by Ard
> Biesheuvel and Steven Rostedt:
> 
>   https://lkml.kernel.org/r/20181005081333.15018-1-ard.biesheuvel@linaro.org
>   https://lkml.kernel.org/r/20181006015110.653946300@goodmis.org
> 
> There are two implementations, depending on arch support:
> 
>  1) out-of-line: patched trampolines (CONFIG_HAVE_STATIC_CALL)
>  2) basic function pointers
> 
> For more details, see the comments in include/linux/static_call.h.
> 
> [peterz: simplified interface]
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve