linux-kernel - Re: [PATCH v6 07/17] static_call: Add inline static call infrastructure

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Date:   Fri, 10 Jul 2020 17:57:05 -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 07/17] static_call: Add inline static call
 infrastructure

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

> From: Josh Poimboeuf <jpoimboe@...hat.com>
> 
> Add infrastructure for an arch-specific CONFIG_HAVE_STATIC_CALL_INLINE
> option, which is a faster version of CONFIG_HAVE_STATIC_CALL.  At
> runtime, the static call sites are patched directly, rather than using
> the out-of-line trampolines.
> 
> Compared to out-of-line static calls, the performance benefits are more
> modest, but still measurable.  Steven Rostedt did some tracepoint
> measurements:
> 
>   https://lkml.kernel.org/r/20181126155405.72b4f718@gandalf.local.home
> 
> This code is heavily inspired by the jump label code (aka "static
> jumps"), as some of the concepts are very similar.
> 
> For more details, see the comments in include/linux/static_call.h.
> 
> [peterz: simplified interface; merged trampolines]
> 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


> ---
>  arch/Kconfig                      |    4 
>  include/asm-generic/vmlinux.lds.h |    7 
>  include/linux/module.h            |    5 
>  include/linux/static_call.h       |   36 ++++
>  include/linux/static_call_types.h |   13 +
>  kernel/Makefile                   |    1 
>  kernel/module.c                   |    5 
>  kernel/static_call.c              |  303 ++++++++++++++++++++++++++++++++++++++
>  8 files changed, 373 insertions(+), 1 deletion(-)
>  create mode 100644 kernel/static_call.c