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[209.132.180.67]) by mx.google.com with ESMTP id b53si3580961edb.419.2019.10.21.08.08.48; Mon, 21 Oct 2019 08:09:17 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=UwNJZsGy; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729435AbfJUPGM (ORCPT + 99 others); Mon, 21 Oct 2019 11:06:12 -0400 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:41677 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727040AbfJUPGM (ORCPT ); Mon, 21 Oct 2019 11:06:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1571670370; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=w1Uk+G0ifBUIpwhzR5PkBxVjQYIPz5NNh0QhaPcxzII=; b=UwNJZsGyVEyhpALJ8ZBdRBSxf8kquHhMLwZ2dRf7JDmiTcFrW2dp8R9KgssiGNXreZDfw8 g1vZ3+lJzrQyW+9mJzu87F0IMas+sds+nzb56zfvs42yf2IgRqu9H5YleaqTNbrjadRhCR nbAHffuWExtgcVv8lU/qi2k/JEDQ4Uc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-253-A_Ae64ZONgmJRM78UBiNUg-1; Mon, 21 Oct 2019 11:06:07 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 381E81005500; Mon, 21 Oct 2019 15:06:05 +0000 (UTC) Received: from treble (ovpn-123-96.rdu2.redhat.com [10.10.123.96]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2FCD0608C0; Mon, 21 Oct 2019 15:05:51 +0000 (UTC) Date: Mon, 21 Oct 2019 10:05:49 -0500 From: Josh Poimboeuf To: Peter Zijlstra Cc: Steven Rostedt , Joe Lawrence , Jessica Yu , Miroslav Benes , x86@kernel.org, linux-kernel@vger.kernel.org, mhiramat@kernel.org, bristot@redhat.com, jbaron@akamai.com, torvalds@linux-foundation.org, tglx@linutronix.de, mingo@kernel.org, namit@vmware.com, hpa@zytor.com, luto@kernel.org, ard.biesheuvel@linaro.org, live-patching@vger.kernel.org Subject: Re: [PATCH v3 5/6] x86/ftrace: Use text_poke() Message-ID: <20191021150549.bitgqifqk2tbd3aj@treble> References: <20191010172819.GS2328@hirez.programming.kicks-ass.net> <20191011125903.GN2359@hirez.programming.kicks-ass.net> <20191015130739.GA23565@linux-8ccs> <20191015135634.GK2328@hirez.programming.kicks-ass.net> <88bab814-ea24-ece9-2bc0-7a1e10a62f12@redhat.com> <20191015153120.GA21580@linux-8ccs> <7e9c7dd1-809e-f130-26a3-3d3328477437@redhat.com> <20191015182705.1aeec284@gandalf.local.home> <20191016074217.GL2328@hirez.programming.kicks-ass.net> MIME-Version: 1.0 In-Reply-To: <20191016074217.GL2328@hirez.programming.kicks-ass.net> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-MC-Unique: A_Ae64ZONgmJRM78UBiNUg-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 16, 2019 at 09:42:17AM +0200, Peter Zijlstra wrote: > > which are not compatible with livepatching. GCC upstream now has > > -flive-patching option, which disables all those interfering optimizati= ons. >=20 > Which, IIRC, has a significant performance impact and should thus really > not be used... >=20 > If distros ship that crap, I'm going to laugh at them the next time they > want a single digit performance improvement because *important*. I have a crazy plan to try to use objtool to detect function changes at a binary level, which would hopefully allow us to drop this flag. But regardless, I wonder if we enabled this flag prematurely. We still don't have a reasonable way to use it for creating source-based live patches upstream, and it should really be optional for CONFIG_LIVEPATCH, since kpatch-build doesn't need it. --=20 Josh