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 D9F80C43613 for ; Thu, 20 Jun 2019 07:15:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B014B2084A for ; Thu, 20 Jun 2019 07:15:25 +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="Hvh03hze" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730545AbfFTHPY (ORCPT ); Thu, 20 Jun 2019 03:15:24 -0400 Received: from merlin.infradead.org ([205.233.59.134]:39460 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725872AbfFTHPX (ORCPT ); Thu, 20 Jun 2019 03:15:23 -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=YLDOeKEFgKiCJoPhKcSOnanWSsPi7sudQNGrpls87Xk=; b=Hvh03hzeGqUCZ23Rsfw22JUI6 D15b+sIQwzRdM/hYgY+rDpSs0Y6SrxJUs1LKWQc1JPVMhIbRJ7foMOn7NgSJFUeyWT0oOd7iLXL5i lmoAVhGfGkzu1UQFezcyyvhwJdSQZqMsy0XHAe8e0XH9ye0jNck0+IRfBvKsXGgTiSkq2Lf4C6q06 T4evu9PuTMaF219uCJSDTfB8cfopDzHV/CRxLVEAOwjY5Lg56kGpWjzCQvVV/f8nKMmLFm+lnKJXA 55LXQbPUwJMRgadEbITW4beOs0lC4tLVykc/xR7U+8T+ceazUUj5KLY6vWeU/d1HJJcaCZciT8s4e TBVAghfkQ==; 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 1hdrHw-0004Bw-4v; Thu, 20 Jun 2019 07:15:16 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id E446F200B4CB3; Thu, 20 Jun 2019 09:15:14 +0200 (CEST) Date: Thu, 20 Jun 2019 09:15:14 +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: <20190620071514.GR3419@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: > FWIW I tried to avoid all of this by using the 2 byte NOP_S and B_S variants which > ensures we can never straddle cache line so the alignment issue goes away. There's > a nice code size reduction too - see [1] . But I get build link errors in > networking code around DO_ONCE where the unlikely code is too much and offset > can't be encoded in signed 10 bits which B_S is allowed. Yeah, so on x86 we have a 2 byte and a 5 byte relative jump and have the exact same issue. We're currently using 5 byte jumps unconditionally for the same reason. Getting it to use the 2 byte one where possible is a 'fun' project for someone with spare time at some point. It might need a GCC plugin to pull off, I've not put too much tought into it.