From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751933Ab2FRN3E (ORCPT ); Mon, 18 Jun 2012 09:29:04 -0400 Received: from casper.infradead.org ([85.118.1.10]:50003 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750756Ab2FRN3C (ORCPT ); Mon, 18 Jun 2012 09:29:02 -0400 Message-ID: <4FDF2D10.9050008@kernel.dk> Date: Mon, 18 Jun 2012 15:28:48 +0200 From: Jens Axboe MIME-Version: 1.0 To: Rob Landley , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: Why does ionice(1) ban the user to set back to 'none' class? References: <20120618114841.GA4855@gmail.com> In-Reply-To: <20120618114841.GA4855@gmail.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/18/2012 01:48 PM, Zheng Liu wrote: > Hi Jens, > > I meet a problem when I use ionice(1) to adjust a process's io priority. > I do the following operations: > > $ ionice -p${pid} > none: prio 0 > $ ionice -p${pid} -c2 -n4 > $ ionice -p${pid} > best-effort: prio 4 > $ ionice -p${pid} -c0 -n0 > $ ionice -p${pid} > best-effort: prio 0 > > So I cannot set scheduling class back to 'none'. If I call ioprio_set(2) > directly, it will be fine. But if I use ionice(1), I cannot change it. I > read the docs about ionice in [1]. I notice this code: > > switch (ioprio_class) { > case IOPRIO_CLASS_NONE: > ioprio_class = IOPRIO_CLASS_BE; > ^^^^^^^^^^^^^^^^ > *It means that we cannot set back to none.* > break; > case IOPRIO_CLASS_RT: > case IOPRIO_CLASS_BE: > break; > case IOPRIO_CLASS_IDLE: > ioprio = 7; > break; > default: > printf("bad prio class %d\n", ioprio_class); > return 1; > } > > My question is why we need to ban the user to set back to 'none'. Is there > some reasons? Thank you. The kernel code does allow it, so it's only in the tool that this restriction exists. I don't think we have a particularly good reason to have it there. This is a tools question, though, not a kernel issue. I suggest you take it up with the util-linux crew. I'm fine with removing this restriction from ionice, especially since you could just roll your own that did it. -- Jens Axboe