From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_2 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 48DD7C433DF for ; Fri, 10 Jul 2020 21:56:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 216532075D for ; Fri, 10 Jul 2020 21:56:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726308AbgGJV4G (ORCPT ); Fri, 10 Jul 2020 17:56:06 -0400 Received: from mail.kernel.org ([198.145.29.99]:60418 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726251AbgGJV4G (ORCPT ); Fri, 10 Jul 2020 17:56:06 -0400 Received: from oasis.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 646B920725; Fri, 10 Jul 2020 21:56:04 +0000 (UTC) Date: Fri, 10 Jul 2020 17:56:02 -0400 From: Steven Rostedt To: Peter Zijlstra Cc: x86@kernel.org, linux-kernel@vger.kernel.org, mhiramat@kernel.org, bristot@redhat.com, jbaron@akamai.com, torvalds@linux-foundation.org, tglx@linutronix.de, mingo@kernel.org, namit@vmware.com, hpa@zytor.com, luto@kernel.org, ard.biesheuvel@linaro.org, jpoimboe@redhat.com, pbonzini@redhat.com, mathieu.desnoyers@efficios.com, linux@rasmusvillemoes.dk Subject: Re: [PATCH v6 06/17] static_call: Add basic static call infrastructure Message-ID: <20200710175602.1a84c355@oasis.local.home> In-Reply-To: <20200710134336.500117453@infradead.org> References: <20200710133831.943894387@infradead.org> <20200710134336.500117453@infradead.org> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 10 Jul 2020 15:38:37 +0200 Peter Zijlstra wrote: > From: Josh Poimboeuf > > 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 > Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Steven Rostedt (VMware) -- Steve