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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_MUTT 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 541D5C43613 for ; Thu, 20 Jun 2019 07:21:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 293FA2084A for ; Thu, 20 Jun 2019 07:21:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="PxDF4z1f" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726693AbfFTHVv (ORCPT ); Thu, 20 Jun 2019 03:21:51 -0400 Received: from merlin.infradead.org ([205.233.59.134]:39530 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726126AbfFTHVv (ORCPT ); Thu, 20 Jun 2019 03:21:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=flv0ZjAK0TpjANrHI4sAx0FN5zH4ci8KQMG+jBdIYOU=; b=PxDF4z1f0ZvO6hgDdo4Rd03Al tyx+x2reUwA9mioDpNaCR2sX77t0seV4VwXFyUjVHa8eQPaHA75HsaWrXlPCl0MgIoUUvrnIauZob pG9lKFb/acLF37vWz4zmYwzuh2Uyf5RMeKJB+foQ6mG/Wm+ym7cSRNMKnvYQp7PxkraKwm6gGbt+N H3Lre1tfXfl1GJQeMBKdaQ+fUesg4+2eUUmUKUhGQeKE0oC2mgt76DlmCuyTWxvApWK0ASFdee7X4 Jo9Ka3CjmW9wzMd2oLh+8LJYTBj1jbeQ3fZkaxbmngMXGv74Nfkei0pxlNoX1S7abhP5Dx9ubhnYC 5m0sCWTIQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1hdrOE-0004G4-0J; Thu, 20 Jun 2019 07:21:46 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id BEEED200B4CB3; Thu, 20 Jun 2019 09:21:44 +0200 (CEST) Date: Thu, 20 Jun 2019 09:21:44 +0200 From: Peter Zijlstra To: Vineet Gupta Cc: Eugeniy Paltsev , "linux-snps-arc@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Alexey Brodkin , Jason Baron , Paolo Bonzini , Ard Biesheuvel , "linux-arch@vger.kernel.org" Subject: Re: [PATCH] ARC: ARCv2: jump label: implement jump label patching Message-ID: <20190620072144.GS3419@hirez.programming.kicks-ass.net> References: <20190614164049.31626-1-Eugeniy.Paltsev@synopsys.com> <20190619081227.GL3419@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 19, 2019 at 11:55:41PM +0000, Vineet Gupta wrote: > So we ensure a patched instruction never crosses a > cache line - using .balign 4. This causes a slight mis-optimization that all > patched instruction locations are forced to be 4 bytes aligned while ISA allows > code to be 2 byte aligned. The cost is an extra NOP_S (2 bytes) - no big deal in > grand scheme of things in IMO. Right, so the scheme x86 uses (which I outlined in an earlier email) allows you to get rid of those extra NOPs. Given jump labels are typically used on fast paths, and NOPs still take up cycles to, at the very least, fetch and decode, some people might care. But if you're OK with having them, then sure, your scheme certainly should work.