From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH, v9 3/3] cgroups: introduce timer slack controller Date: Mon, 14 Mar 2011 16:46:52 -0700 Message-ID: <20110314164652.5b44fb9e.akpm@linux-foundation.org> References: <1300111524-5666-1-git-send-email-kirill@shutemov.name> <1300111524-5666-4-git-send-email-kirill@shutemov.name> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1300111524-5666-4-git-send-email-kirill-oKw7cIdHH8eLwutG50LtGA@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: "Kirill A. Shutemov" Cc: Paul Menage , Li Zefan , Thomas Gleixner , containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, jacob.jun.pan-VuQAYsv1563Yd54FQh9/CA@public.gmane.org, Arjan van de Ven , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Matt Helsley , linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-api@vger.kernel.org On Mon, 14 Mar 2011 16:05:24 +0200 Kirill A. Shutemov" wrote: > +Overview > +-------- > + > +Every task_struct has timer_slack_ns value. This value uses to round up > +poll() and select() timeout values. This feature can be useful in > +mobile environment where combined wakeups are desired. > + > +Originally, prctl() was the only way to change timer slack value of > +a process. So you was not able change timer slack value of another > +process. > + > +cgroup subsys "timer_slack" implements timer slack controller. It > +provides a way to set minimal timer slack value for a group of tasks. > +If a task belongs to a cgroup with minimal timer slack value higher than > +task's value, cgroup's value will be applied. > + > +Timer slack controller allows to implement setting timer slack value of > +a process based on a policy. For example, you can create foreground and > +background cgroups and move tasks between them based on system state. (quoting myself from last time) Why do we need a cgroup for this as opposed to (say) inheritance over fork(), or a system-wide knob, or a per-process/threadgroup knob, or just leaving the existing code as-is? Presumably you felt that a cgroup approach is better for manageability, but you didn't tell us about this and you didn't explore alternative ways of solving the problem-which-you-didn't-describe. I'm still having trouble seeing why we should merge this. Who will use it, and for what reason and what benefits will they see? Quantified benefits, if possible!