Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752387Ab1BFCt6 (ORCPT <rfc822;w@1wt.eu>);
	Sat, 5 Feb 2011 21:49:58 -0500
Received: from e34.co.us.ibm.com ([32.97.110.152]:54681 "EHLO
	e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751640Ab1BFCt5 (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Sat, 5 Feb 2011 21:49:57 -0500
Date: Sat, 5 Feb 2011 18:49:51 -0800
From: Matt Helsley <matthltc@us.ibm.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Matt Helsley <matthltc@us.ibm.com>, Paul Menage <menage@google.com>,
        Li Zefan <lizf@cn.fujitsu.com>, containers@lists.linux-foundation.org,
        jacob.jun.pan@linux.intel.com,
        Arjan van de Ven <arjan@linux.intel.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH, v3 2/2] cgroups: introduce timer slack subsystem
Message-ID: <20110206024951.GB16432@count0.beaverton.ibm.com>
References: <1296679656-31163-1-git-send-email-kirill@shutemov.name>
 <1296679656-31163-3-git-send-email-kirill@shutemov.name>
 <20110203054616.GT16432@count0.beaverton.ibm.com>
 <20110203094138.GD1083@shutemov.name>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20110203094138.GD1083@shutemov.name>
User-Agent: Mutt/1.5.20 (2009-06-14)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 2121
Lines: 57

On Thu, Feb 03, 2011 at 11:41:38AM +0200, Kirill A. Shutemov wrote:
> On Wed, Feb 02, 2011 at 09:46:16PM -0800, Matt Helsley wrote:
> > On Wed, Feb 02, 2011 at 10:47:36PM +0200, Kirill A. Shutsemov wrote:
> > > From: Kirill A. Shutemov <kirill@shutemov.name>

<snip>

> > > diff --git a/kernel/cgroup_timer_slack.c b/kernel/cgroup_timer_slack.c
> > > new file mode 100644
> > > index 0000000..a343a50
> > > --- /dev/null
> > > +++ b/kernel/cgroup_timer_slack.c

<snip>

> > > +static int tslack_write_set_slack_ns(struct cgroup *cgroup, struct cftype *cft,
> > > +		u64 val)
> > > +{
> > > +	struct timer_slack_cgroup *tslack_cgroup;
> > > +	struct cgroup_iter it;
> > > +	struct task_struct *task;
> > > +
> > > +	tslack_cgroup = cgroup_to_tslack_cgroup(cgroup);
> > > +	if (!val || val < tslack_cgroup->min_slack_ns ||
> > 
> > Why is a val of 0 disallowed? I know having slack is good, but for
> > an administrator or tool that doesn't care about number of wakeups
> > and cares more about wringing out performance a slack of
> > 0 seems acceptable. Is this just here to be consistent with the
> > values passed in via prctl?
> 
> Yes, it's to consistent with the prctl(). I don't think that it's good
> idea to allow to set timer_slack outside of range prctl() allows. It may
> lead to interface abuse.

Hmm, I was just thinking that 0 timer slack might be useful. But I
suppose you could just as easily set it to 1 and nobody would notice.

> > > +			val > tslack_cgroup->max_slack_ns )
> > > +		return -EINVAL;
> > 
> > Shouldn't it be EPERM and not EINVAL?
> > 
> > The write(2) man page says: "Other errors may occur, depending on the
> > object connected to fd." So I think EPERM is fine and more descriptive.
> 
> What do you think about -EINVAL for (val == 0) and -EPERM for rest?

OK, that makes sense to me given both of our points above.

Cheers,
	-Matt Helsley
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/