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=-6.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT 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 B833EC43381 for ; Tue, 26 Mar 2019 18:03:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 997F32084B for ; Tue, 26 Mar 2019 18:03:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732386AbfCZSDz (ORCPT ); Tue, 26 Mar 2019 14:03:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53752 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731940AbfCZSDz (ORCPT ); Tue, 26 Mar 2019 14:03:55 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E6D163004E7B; Tue, 26 Mar 2019 18:03:54 +0000 (UTC) Received: from treble (ovpn-120-253.rdu2.redhat.com [10.10.120.253]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C7A6C5C72F; Tue, 26 Mar 2019 18:03:51 +0000 (UTC) Date: Tue, 26 Mar 2019 13:03:48 -0500 From: Josh Poimboeuf To: Thomas Gleixner Cc: linux-kernel@vger.kernel.org, x86@kernel.org, Andrea Arcangeli , Waiman Long , Peter Zijlstra , Jiri Kosina Subject: Re: [PATCH] cpu/hotplug: Create SMT sysfs interface for all arches Message-ID: <20190326180348.fzerpltlf62dnurd@treble> References: <426cde0f727f0cbadc501bb9bca8c99c4e11ac02.1551462051.git.jpoimboe@redhat.com> <20190326133236.lylrrbacznezybjm@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.47]); Tue, 26 Mar 2019 18:03:55 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 26, 2019 at 02:53:04PM +0100, Thomas Gleixner wrote: > On Tue, 26 Mar 2019, Josh Poimboeuf wrote: > > On Sun, Mar 24, 2019 at 09:13:18PM +0100, Thomas Gleixner wrote: > > > Second thoughts. I'm not really convinced that changing the meaning of > > > notsupported and in fact overloading it, is the right thing to do. > > > notsupported means now: > > > > > > CPU does not support it - OR - architecture does not support it > > > > > > That's not pretty and we are surely not short of state space. There are > > > several options for handling this: > > > > > > 1) Do not expose the state file, just expose the active file > > > > > > 2) Expose the state file, but return -ENOTSUPP or some other sensible error > > > code > > > > > > 3) Expose the state file and let show return 'notimplemented' which is > > > more accurate. That wouldn't even require to expand the state space > > > enum. It just can be returned unconditionally. > > > > Makes sense. I like #3. I can post another version. > > Yes, please. Something like so (on top of the original patch)? diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu index 4a11cba73085..5eea46fefcb2 100644 --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -511,11 +511,12 @@ Description: Control Symetric Multi Threading (SMT) control: Read/write interface to control SMT. Possible values: - "on" SMT is enabled - "off" SMT is disabled - "forceoff" SMT is force disabled. Cannot be changed. - "notsupported" Runtime SMT toggling is not currently - supported for the architecture + "on" SMT is enabled + "off" SMT is disabled + "forceoff" SMT is force disabled. Cannot be changed. + "notsupported" SMT is not supported by the CPU + "notimplemented" SMT runtime toggling is not + implemented for the architecture If control status is "forceoff" or "notsupported" writes are rejected. diff --git a/kernel/cpu.c b/kernel/cpu.c index 517ab1803a22..05a71ee98440 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -2145,7 +2145,11 @@ static const char *smt_states[] = { static ssize_t show_smt_control(struct device *dev, struct device_attribute *attr, char *buf) { - return snprintf(buf, PAGE_SIZE - 2, "%s\n", smt_states[cpu_smt_control]); + const char *state = IS_ENABLED(CONFIG_HOTPLUG_SMT) ? + smt_states[cpu_smt_control] : + "notimplemented"; + + return snprintf(buf, PAGE_SIZE - 2, "%s\n", state); } static ssize_t