From mboxrd@z Thu Jan 1 00:00:00 1970 From: Patrick Bellasi Subject: Re: [PATCH v5 07/15] sched/core: uclamp: add clamp group bucketing support Date: Tue, 13 Nov 2018 07:29:48 -0800 Message-ID: <20181113152948.GC7681@darkstar> References: <20181029183311.29175-1-patrick.bellasi@arm.com> <20181029183311.29175-9-patrick.bellasi@arm.com> <20181112000910.GC3038@worktop> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20181112000910.GC3038@worktop> Sender: linux-kernel-owner@vger.kernel.org To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Ingo Molnar , Tejun Heo , "Rafael J . Wysocki" , Vincent Guittot , Viresh Kumar , Paul Turner , Quentin Perret , Dietmar Eggemann , Morten Rasmussen , Juri Lelli , Todd Kjos , Joel Fernandes , Steve Muckle , Suren Baghdasaryan List-Id: linux-pm@vger.kernel.org On 12-Nov 01:09, Peter Zijlstra wrote: > On Mon, Oct 29, 2018 at 06:33:02PM +0000, Patrick Bellasi wrote: > > The number of clamp groups configured at compile time defines the range > > of utilization clamp values tracked by each CPU clamp group. > > For example, with the default configuration: > > CONFIG_UCLAMP_GROUPS_COUNT 5 > > we will have 5 clamp groups tracking 20% utilization each. In this case, > > a task with util_min=25% will have group_id=1. > > OK I suppose; but should we not do a wholesale s/group/bucket/ at this > point? Yes, if bucketization is acceptable, we should probably rename. Question is: are you ok for a renaming in this patch. or you better prefer I use that naming since the beginning ? If we wanna use "bucket" since the beginning, then we should also probably squash the entire patch into the previous ones and drop this one. I personally prefer to keep this concept into a separate patch, but at the same time I don't very like the idea of a massive renaming in this patch. > > We should probably raise the minimum number of buckets from 1 though :-) Mmm... the default is already set to what fits into a single cache line... perhaps we can use that as a minimum too ? But. technically we can (partially) track different clamp values also with just one bucket... (explanation in the following comment). > > +/* > > + * uclamp_group_value: get the "group value" for a given "clamp value" > > + * @value: the utiliation "clamp value" to translate > > + * > > + * The number of clamp group, which is defined at compile time, allows to > > + * track a finite number of different clamp values. Thus clamp values are > > + * grouped into bins each one representing a different "group value". > > + * This method returns the "group value" corresponding to the specified > > + * "clamp value". > > + */ > > +static inline unsigned int uclamp_group_value(unsigned int clamp_value) > > +{ > > +#define UCLAMP_GROUP_DELTA (SCHED_CAPACITY_SCALE / CONFIG_UCLAMP_GROUPS_COUNT) > > +#define UCLAMP_GROUP_UPPER (UCLAMP_GROUP_DELTA * CONFIG_UCLAMP_GROUPS_COUNT) > > + > > + if (clamp_value >= UCLAMP_GROUP_UPPER) > > + return SCHED_CAPACITY_SCALE; > > + > > + return UCLAMP_GROUP_DELTA * (clamp_value / UCLAMP_GROUP_DELTA); > > +} > > Can't we further simplify; I mean, at this point all we really need to > know is the rq's highest group_id that is in use. We don't need to > actually track the value anymore. This will force to track each clamp value with the exact bucket value. Instead, by tracking the actual clamp value within a bucket, we have the chance to updte the bucket value to the actual (max) clamp value of the RUNNABLE tasks in that bucket. In a properly configured system, this allows to track exact clamp values with a minimum number of buckets. -- #include Patrick Bellasi