From: Peter Zijlstra <firstname.lastname@example.org> To: Douglas Raillard <email@example.com> Cc: firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org Subject: Re: [RFC PATCH v3 0/6] sched/cpufreq: Make schedutil energy aware Date: Thu, 17 Oct 2019 21:07:08 +0200 Message-ID: <20191017190708.GF22902@worktop.programming.kicks-ass.net> (raw) In-Reply-To: <email@example.com> On Thu, Oct 17, 2019 at 03:23:04PM +0100, Douglas Raillard wrote: > On 10/17/19 10:50 AM, Peter Zijlstra wrote: > > I'm still thinking about the exact means you're using to raise C; that > > is, the 'util - util_est' as cost_margin. It hurts my brain still. > > util_est is currently the best approximation of the actual portion of the CPU the task needs: > 1) for periodic tasks, it's not too far from the duty cycle, and is always higher > > 2) for aperiodic tasks, it (indirectly) takes into account the total time it took > to complete the previous activation, so the signal is not 100% composed of logical signals > only relevant for periodic tasks (although it's a big part of it). > > 3) Point 1) and 2) together allows util_est to adapt to periodic tasks that changes > their duty cycle over time, without needing a very long history (the last task period > is sufficient). > > For periodic tasks, the distance between instantaneous util_avg and the actual task > duty cycle indicates somehow what is our best guess of the (potential) change in the task > duty cycle. > > util_est is the threshold (assuming util_avg increasing) for util_avg after which we know > for sure that even if the task stopped right now, its duty cycle would be higher than > during the previous period. > This means for a given task and with (util >= util_est): > > 1) util - util_est == 0 means the task duty cycle will be equal to the one during > during the previous activation, if the tasks stopped executing right now. > > 2) util - util_est > 0 means the task duty cycle will be higher to the one during > during the previous activation, if the tasks stopped executing right now. So far I can follow, 2) is indeed a fairly sane indication that utilization is growing. > Using the difference (util - util_est) will therefore give these properties to the boost signal: > * no boost will be applied as long as the task has a constant or decreasing duty cycle. > > * when we can detect that the duty cycle increases, we temporarily increase the frequency. > We start with a slight increase, and the longer we wait for the current period to finish, > the more we boost, since the more likely it is that the task has a much larger duty cycle > than anticipated. More specifically, the evaluation of "how much more" is done the exact > same way as it is done for PELT, since the dynamic of the boost is "inherited" from PELT. Right, because as long it keeps running, util_est will not be changed, so the difference will continue to increase. What I don't see is how that that difference makes sense as input to: cost(x) : (1 + x) * cost_j I suppose that limits the additional OPP to twice the previously selected cost / efficiency (see the confusion from that other email). But given that efficency drops (or costs rise) for higher OPPs that still doesn't really make sense.. > Now if the task is aperiodic, the boost will allow reaching the highest frequency faster, > which may or may not be desired. Ultimately, it's not more or less wrong than just picking > the freq based on util_est alone, since util_est is already somewhat meaningless for aperiodic > tasks. It just allows reaching the max freq at some point without waiting for too long, which is > all what we can do without more info on the task. > > When applying these boosting rules on the runqueue util signals, we are able to detect if at least one > task needs boosting according to these rules. That only holds as long as the history we look at is > the result of a stable set of tasks, i.e. no tasks added or removed from the rq. So while I agree that 2) is a reasonable signal to work from, everything that comes after is still much confusing me.
next prev parent reply index Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-10-11 13:44 Douglas RAILLARD 2019-10-11 13:44 ` [RFC PATCH v3 1/6] PM: Introduce em_pd_get_higher_freq() Douglas RAILLARD 2019-10-17 8:57 ` Dietmar Eggemann 2019-10-17 9:58 ` Dietmar Eggemann 2019-10-17 11:09 ` Douglas Raillard 2019-10-11 13:44 ` [RFC PATCH v3 2/6] sched/cpufreq: Attach perf domain to sugov policy Douglas RAILLARD 2019-10-17 8:57 ` Dietmar Eggemann 2019-10-17 10:22 ` Douglas Raillard 2019-10-11 13:44 ` [RFC PATCH v3 3/6] sched/cpufreq: Hook em_pd_get_higher_power() into get_next_freq() Douglas RAILLARD 2019-10-11 13:44 ` [RFC PATCH v3 4/6] sched/cpufreq: Introduce sugov_cpu_ramp_boost Douglas RAILLARD 2019-10-14 14:33 ` Peter Zijlstra 2019-10-14 15:32 ` Douglas Raillard 2019-10-17 8:57 ` Dietmar Eggemann 2019-10-17 11:19 ` Douglas Raillard 2019-10-11 13:44 ` [RFC PATCH v3 5/6] sched/cpufreq: Boost schedutil frequency ramp up Douglas RAILLARD 2019-10-17 9:21 ` Dietmar Eggemann 2019-10-11 13:45 ` [RFC PATCH v3 6/6] sched/cpufreq: Add schedutil_em_tp tracepoint Douglas RAILLARD 2019-10-14 14:53 ` [RFC PATCH v3 0/6] sched/cpufreq: Make schedutil energy aware Peter Zijlstra 2019-10-14 15:50 ` Douglas Raillard 2019-10-17 9:50 ` Peter Zijlstra 2019-10-17 11:11 ` Quentin Perret 2019-10-17 14:11 ` Peter Zijlstra 2019-10-18 7:44 ` Dietmar Eggemann 2019-10-18 7:59 ` Peter Zijlstra 2019-10-18 17:24 ` Douglas Raillard 2019-10-18 8:11 ` Peter Zijlstra 2019-10-17 14:23 ` Douglas Raillard 2019-10-17 14:53 ` Peter Zijlstra 2019-10-17 19:07 ` Peter Zijlstra [this message] 2019-10-18 11:46 ` Douglas Raillard 2019-10-18 12:07 ` Peter Zijlstra 2019-10-18 14:44 ` Douglas Raillard 2019-10-18 15:15 ` Vincent Guittot 2019-10-18 16:03 ` Douglas Raillard 2019-10-18 15:20 ` Vincent Guittot
Reply instructions: You may reply publically to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20191017190708.GF22902@worktop.programming.kicks-ass.net \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
Linux-PM Archive on lore.kernel.org Archives are clonable: git clone --mirror https://lore.kernel.org/linux-pm/0 linux-pm/git/0.git # If you have public-inbox 1.1+ installed, you may # initialize and index your mirror using the following commands: public-inbox-init -V2 linux-pm linux-pm/ https://lore.kernel.org/linux-pm \ email@example.com public-inbox-index linux-pm Example config snippet for mirrors Newsgroup available over NNTP: nntp://nntp.lore.kernel.org/org.kernel.vger.linux-pm AGPL code for this site: git clone https://public-inbox.org/public-inbox.git