Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751358AbaKFQ1T (ORCPT ); Thu, 6 Nov 2014 11:27:19 -0500 Received: from mail-wg0-f43.google.com ([74.125.82.43]:56922 "EHLO mail-wg0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750877AbaKFQ1S (ORCPT ); Thu, 6 Nov 2014 11:27:18 -0500 Date: Thu, 6 Nov 2014 16:27:13 +0000 From: Matt Fleming To: Peter Zijlstra Cc: Tejun Heo , Vikas Shivappa , "Auld, Will" , Vikas Shivappa , "linux-kernel@vger.kernel.org" , "Fleming, Matt" Subject: Re: Cache Allocation Technology Design Message-ID: <20141106162713.GI3592@console-pimps.org> References: <20141029172845.GP12706@worktop.programming.kicks-ass.net> <20141029182234.GA13393@mtj.dyndns.org> <20141030070725.GG3337@twins.programming.kicks-ass.net> <20141030124333.GA29540@htj.dyndns.org> <20141030131845.GI3337@twins.programming.kicks-ass.net> <20141030170331.GB378@htj.dyndns.org> <20141030214353.GB12706@worktop.programming.kicks-ass.net> <20141030222236.GD378@htj.dyndns.org> <20141030224740.GC12706@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141030224740.GC12706@worktop.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 30 Oct, at 11:47:40PM, Peter Zijlstra wrote: > > Let me reply to just this one, I'll do the rest tomorrow, need sleeps. > > On Thu, Oct 30, 2014 at 06:22:36PM -0400, Tejun Heo wrote: > > > > > This controller might not even require the distinction between > > > > configured and effective tho? Can't a new child just inherit the > > > > parent's configuration and never allow the config to become completely > > > > empty? > > > > > > It can do that. But that still has a problem, there is a mapping in > > > hardware which restricts the number of active configurations. The total > > > configuration space is larger than the supported active configurations. > > > > > > So _something_ must fail. The initial proposal was mkdir failing when > > > there were more than the hardware supported active config cgroup > > > directories. The alternative was on-demand activation where we only > > > allocate the hardware resource when the first task gets moved into the > > > group -- which then clearly can fail. > > > > Hmmm... why can't it just refuse creating a different configuration > > when its config space is full? Make children inherit the parent's > > configuration and refuse config writes which require it to create a > > new one if the config space is full. Seems pretty straight-forward. > > What am I missing? > > We could do that I suppose, there is the one corner case that would not > allow, intermediate directories with a restricted config that also have > priv restrictions but no actual tasks. Not sure that makes sense though. Could you elaborate on this configuration? > Are there any other cases I might have missed? I don't think so. So, for the specific CAT case what you're proposing is make the failure case happen when writing to the cache bitmask file instead of failing mkdir() or echo $tid > tasks ? I think that's OK. If we've run out of CLOS ids I would expect to see -ENOSPC returned, whereas if we try and set an invalid bitmask we'd get -EINVAL. Vikas, Will? -- Matt Fleming, Intel Open Source Technology Center -- 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/