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=-3.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 53EF0C2D0A3 for ; Thu, 29 Oct 2020 11:46:25 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C996B20780 for ; Thu, 29 Oct 2020 11:46:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="j8qs7I7a" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C996B20780 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Iizh9zj0tLTR295ftwb03g29063JN2c+/hOGIKAYl8Y=; b=j8qs7I7a7Kfz7g6gbri46TAEU yqMkmzE5bS1L+2iQNV2f03u4dbSq37mBbY9Pbjul2BKhjh7hdukgH9TBJnwAcdL6RK1UUoiAWfbiC uo9nYk0MGJRIUbfO8goF63zaf22iIEabPX9lcpt0Ic1+MwOIKr57rvUh0rgaNTtjQrNHeMhpYtJhm vbQNxfP0oSdcR/nQ3+SecohizfpPGB4d+h7quVQArRyOEOhJA02hjs9N48TCnoPOeVGofIz58/9+/ wRX7ihzmS5OSfP+dbYubCnbU2wC/EF81DNUettWyQoLjjrsQLtLmZ0XV8KDzKmhT6EhF1lfB0z+mS yUO/gM2SQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kY6MZ-0003A5-PJ; Thu, 29 Oct 2020 11:45:03 +0000 Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kY6MX-00039W-GK; Thu, 29 Oct 2020 11:45:01 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 7E7743012C3; Thu, 29 Oct 2020 12:44:57 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 6ACD92C2F3324; Thu, 29 Oct 2020 12:44:57 +0100 (CET) Date: Thu, 29 Oct 2020 12:44:57 +0100 From: Peter Zijlstra To: Ard Biesheuvel Subject: Re: [PATCH v2] arm64: implement support for static call trampolines Message-ID: <20201029114457.GL2628@hirez.programming.kicks-ass.net> References: <20201028184114.6834-1-ardb@kernel.org> <20201029112747.GA4090840@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Quentin Perret , Catalin Marinas , Steven Rostedt , James Morse , Will Deacon , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Oct 29, 2020 at 12:32:50PM +0100, Ard Biesheuvel wrote: > However, as I discussed with Will offline yesterday as well, the > question that got snowed under is whether we need any of this on arm64 > in the first place. It seems highly unlikely that inline static calls > are worth it, and even out-of-line static calls are probably not worth > the hassle as we don't have the retpoline problem. > > So this code should be considered an invitation for discussion, and > perhaps someone can invent a use case where benchmarks can show a > worthwhile improvement. But let's not get ahead of ourselves. So the obvious benefit is not having to do the extra load. Any indirect call will have to do a load first, which can miss etc.. And yes, retpoline is a horrible mess as well. Doing the direct vs indirect saves one I$ miss I suppose, which can be noticable. IIRC Steve had benchmarks for the ftrace conversion, which is now upstream, so that should be simple enough to run. Steve, remember how to get numbers out of that? _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel