From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH 0/4] x86: Add Cache QoS Monitoring (CQM) support Date: Mon, 6 Jan 2014 19:06:36 +0100 Message-ID: <20140106180636.GG30183@twins.programming.kicks-ass.net> References: <1388781285-18067-1-git-send-email-peter.p.waskiewicz.jr@intel.com> <20140104161050.GA24306@htj.dyndns.org> <1388875369.9761.25.camel@ppwaskie-mobl.amr.corp.intel.com> <20140104225058.GC24306@htj.dyndns.org> <1388899376.9761.45.camel@ppwaskie-mobl.amr.corp.intel.com> <20140106111624.GB5623@twins.programming.kicks-ass.net> <1389026035.32504.3.camel@ppwaskie-mobl.amr.corp.intel.com> <20140106164150.GQ31570@twins.programming.kicks-ass.net> <1389026867.32504.16.camel@ppwaskie-mobl.amr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1389026867.32504.16.camel-29DAm2eTeB2q+SSgkFU3IPooFf0ArEBIu+b9c/7xato@public.gmane.org> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: "Waskiewicz Jr, Peter P" Cc: "containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Ingo Molnar , "H. Peter Anvin" , Tejun Heo , "cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Thomas Gleixner On Mon, Jan 06, 2014 at 04:47:57PM +0000, Waskiewicz Jr, Peter P wrote: > > As is I don't really see a good use for RMIDs and I would simply not use > > them. > > If you want to use CQM in the hardware, then the RMID is how you get the > cache usage data from the CPU. If you don't want to use CQM, then you > can ignore RMIDs. I think you can make do with a single RMID (per cpu). When you program the counter (be it for a task, cpu or cgroup context) you set the 1 RMID and EVSEL and read the CTR. What I'm not entirely clear on is if the EVSEL and CTR MSR are per logical CPU or per L3 (package); /me prays they're per logical CPU. > One of the best use cases for using RMIDs is in virtualization. *groan*.. /me plugs wax in ears and goes la-la-la-la > A VM > may be a heavy cache user, or a light cache user. Tracing different VMs > on different RMIDs can allow an admin to identify which VM may be > causing high levels of eviction, and either migrate it to another host, > or move other tasks/VMs to other hosts. Without CQM, it's much harder > to find which process is eating the cache up. Not necessarily VMs, there's plenty large processes that exhibit similar problems.. why must people always do VMs :-( That said, even with a single RMID you can get that information by simply running it against all competing processes one at a time. Since there's limited RMID space you need to rotate at some point anyway. The cgroup interface you propose wouldn't allow for rotation; other than manual by creating different cgroups one after another.