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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 1F4F3C43381 for ; Mon, 1 Apr 2019 11:10:18 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 92B8C20870 for ; Mon, 1 Apr 2019 11:10:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 92B8C20870 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 44XqPg0rqJzDqMh for ; Mon, 1 Apr 2019 22:10:15 +1100 (AEDT) Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 44XqMm498KzDqL4 for ; Mon, 1 Apr 2019 22:08:36 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mail.ozlabs.org (Postfix) with ESMTPSA id 44XqMj2fSxz9sQr; Mon, 1 Apr 2019 22:08:31 +1100 (AEDT) From: Michael Ellerman To: Andrey Abramov , vgupta , benh , paulus , tglx , mingo , bp , hpa , x86 , mark , jlbec , richard , dedekind1 , "adrian.hunter" , gregkh , "naveen.n.rao" , jpoimboe , Dave Chinner , "darrick.wong" , "ard.biesheuvel" , George Spelvin , linux-snps-arc , Linux Kernel Mailing List , linuxppc-dev , ocfs2-devel , linux-mtd , sfr Subject: Re: [PATCH v2 2/5] powerpc: module_[32|64].c: replace swap function with built-in one In-Reply-To: <14019281554057359@sas1-87f9feb8d943.qloud-c.yandex.net> References: <19606671554056883@myt3-1179f584969c.qloud-c.yandex.net> <14019281554057359@sas1-87f9feb8d943.qloud-c.yandex.net> Date: Mon, 01 Apr 2019 22:08:30 +1100 Message-ID: <87v9zyoudt.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: malat , "yamada.masahiro" , npiggin Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Andrey Abramov writes: > Replace relaswap with built-in one, because relaswap > does a simple byte to byte swap. I replied to v1 with an ack, which stands, this is just a clarification. > Since Spectre mitigations have made indirect function calls more > expensive, and the default simple byte copies swap is implemented > without them, an "optimized" custom swap function is now > a waste of time as well as code. Spectre mitigations don't necessarily slow down indirect function calls on all arches or in all configurations on all arches, so that justification is a bit dubious. That's not really a problem for this patch, because the existing overhead of the function call is probably already enough to rival the cost of the 24 byte copy. cheers