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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED autolearn=ham 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 56134C43381 for ; Mon, 1 Apr 2019 11:08:48 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 2768E20870 for ; Mon, 1 Apr 2019 11:08:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="nC4YzwiH" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2768E20870 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-mtd-bounces+linux-mtd=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:Message-ID:Date:References :In-Reply-To:Subject:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=e6kv19+YQrLnDecI23sFp5aOZObSnnioW4209HUojFc=; b=nC4YzwiHWk1auf o40wr/KmHatUv4B7OGCA+oIpkiq3jJiFjsIP+LuiMpNIR4BCjWK9ebITo7fl92+uPuO1iF2VXYWM1 T7xHMHGl1y67w2e8AeNqU9hrEpDo9whBzJ0uixngOpmOjMEu+zQTlnrIQxq9ViCYywq43RRwpPqOF gUONOVe4oBLXmnZcVPnaJOVzgcmz69qQj/eYTr3PxI7uOnJDN8qFsWEARqx2eFZjSZoRVgmp1XnoR FMhhrJ08DXeZazSQyP5xTyQ4WbTK/1LCc6nWoFdboiV1vwvh+KaYkgQbbmic73XmJF3GNaMlLBKMO fbDdGR+E4QELk8rwKurg==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hAuo2-0002gJ-5r; Mon, 01 Apr 2019 11:08:46 +0000 Received: from ozlabs.org ([2401:3900:2:1::2]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1hAunx-0002fG-KD; Mon, 01 Apr 2019 11:08:45 +0000 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190401_040841_906263_71642859 X-CRM114-Status: UNSURE ( 6.10 ) X-CRM114-Notice: Please train this message. X-BeenThere: linux-mtd@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: malat , "yamada.masahiro" , npiggin Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-mtd" Errors-To: linux-mtd-bounces+linux-mtd=archiver.kernel.org@lists.infradead.org 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 ______________________________________________________ Linux MTD discussion mailing list http://lists.infradead.org/mailman/listinfo/linux-mtd/