From: Patrick Bellasi <patrick.bellasi@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
Juri Lelli <juri.lelli@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@suse.de>,
Len Brown <lenb@kernel.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Mel Gorman <mgorman@techsingularity.net>,
the arch/x86 maintainers <x86@kernel.org>,
Linux PM <linux-pm@vger.kernel.org>,
Viresh Kumar <viresh.kumar@linaro.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC/RFT] [PATCH 02/10] cpufreq: intel_pstate: Conditional frequency invariant accounting
Date: Wed, 30 May 2018 17:57:34 +0100 [thread overview]
Message-ID: <20180530165734.GL30654@e110439-lin> (raw)
In-Reply-To: <20180518133353.GO30654@e110439-lin>
Hi Peter,
maybe you missed this previous my response:
20180518133353.GO30654@e110439-lin
?
Would like to have your tought about the concept of "transient maximum
capacity" I was describing...
On 18-May 14:33, Patrick Bellasi wrote:
> On 18-May 13:29, Peter Zijlstra wrote:
> > On Fri, May 18, 2018 at 11:57:42AM +0100, Patrick Bellasi wrote:
> > > Thus, my simple (maybe dumb) questions are:
> > > - why can't we just fold turbo boost frequency into the existing concepts?
> > > - what are the limitations of such a "simple" approach?
> >
> > Perhaps... but does this not further complicate the whole capacity vs
> > util thing we already have in say the misfit patches?
>
> Not sure about that...
>
> > And the util_fits_capacity() thing from the EAS ones.
>
> In this case instead, if we can track somehow (not saying we can)
> what is the currently available "transient maximum capacity"...
> then a util_fits_capacity() should just look at that.
>
> If the transient capacity is already folded into cpu_capacity, as it
> is now for RT and IRQ pressure, then likely we don't have to change
> anything.
>
> > The thing is, we either need to dynamically scale the util or the
> > capacity or both. I think for Thermal there are patches out there that
> > drop the capacity.
>
> Not sure... but I would feel more comfortable by something which caps
> the maximum capacity. Meaning, eventually you can fill up the maximum
> possible capacity only "up to" a given value, because of thermal or other
> reasons most of the scheduler maybe doesn't even have to know why?
>
> > But we'd then have to do the same for turbo/vector and all the other
> > stuff as well. Otherwise we risk things like running at low U with 0%
> > idle and not triggering the tipping point between eas and regular
> > balancing.
>
> Interacting with the tipping point and/or OPP changes is indeed an
> interesting side of the problem I was not considering so far...
>
> But again, the tipping point could not be defined as a delta
> with respect to the "transient maximum capacity" ?
>
> > So either way around we need to know the 'true' max, either to fudge
> > util or to fudge capacity.
>
> Right, but what I see from a concepts standpoint is something like:
>
> +--+--+ cpu_capacity_orig (CONSTANT at boot time)
> | | |
> | | | HW generated constraints
> | v |
> +-----+ cpu_capacity_max (depending on thermal/turbo boost)
> | | |
> | | | SW generated constraints
> | v |
> +-----+ cpu_capacity (depending on RT/IRQ pressure)
> | | |
> | | | tipping point delta
> +--v--+
> | | Energy Aware mode available capacity
> +-----+
>
> Where all the wkp/lb heuristics are updated to properly consider the
> cpu_capacity_max metrics whenever it comes to know what is the max
> speed we can reach now on a CPU.
>
> > And I'm not sure we can know in some of these cases :/
>
> Right, this schema will eventually work only under the hypothesis that
> "somehow" we can update cpu_capacity_max from HW events.
>
> Not entirely sure that's possible and/or at which time granularity on
> all different platforms.
>
> > And while Vincent's patches might have been inspired by another problem,
> > they do have the effect of always allowing util to go to 1, which is
> > nice for this.
>
> Sure, that's a nice point, but still I have the feeling that always
> reaching u=1 can defeat other interesting properties of a task,
> For example, comparing task requirements in different CPUs and/or at
> different times, which plays a big role for energy aware task
> placement decisions.
>
> --
> #include <best/regards.h>
>
> Patrick Bellasi
--
#include <best/regards.h>
Patrick Bellasi
next prev parent reply other threads:[~2018-05-30 16:57 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-16 4:49 [RFC/RFT] [PATCH 00/10] Intel_pstate: HWP Dynamic performance boost Srinivas Pandruvada
2018-05-16 4:49 ` [RFC/RFT] [PATCH 01/10] x86,sched: Add support for frequency invariance Srinivas Pandruvada
2018-05-16 9:56 ` Peter Zijlstra
2018-05-16 4:49 ` [RFC/RFT] [PATCH 02/10] cpufreq: intel_pstate: Conditional frequency invariant accounting Srinivas Pandruvada
2018-05-16 7:16 ` Peter Zijlstra
2018-05-16 7:29 ` Peter Zijlstra
2018-05-16 9:07 ` Rafael J. Wysocki
2018-05-16 17:32 ` Srinivas Pandruvada
2018-05-16 15:19 ` Juri Lelli
2018-05-16 15:47 ` Peter Zijlstra
2018-05-16 16:31 ` Juri Lelli
2018-05-17 10:59 ` Juri Lelli
2018-05-17 15:04 ` Juri Lelli
2018-05-17 15:41 ` Srinivas Pandruvada
2018-05-17 16:16 ` Peter Zijlstra
2018-05-17 16:42 ` Srinivas Pandruvada
2018-05-17 16:56 ` Rafael J. Wysocki
2018-05-17 18:28 ` Peter Zijlstra
2018-05-18 7:36 ` Rafael J. Wysocki
2018-05-18 10:57 ` Patrick Bellasi
2018-05-18 11:29 ` Peter Zijlstra
2018-05-18 13:33 ` Patrick Bellasi
2018-05-30 16:57 ` Patrick Bellasi [this message]
2018-05-18 14:09 ` Valentin Schneider
2018-05-16 15:58 ` Srinivas Pandruvada
2018-05-16 4:49 ` [RFC/RFT] [PATCH 03/10] cpufreq: intel_pstate: Utility functions to boost HWP performance limits Srinivas Pandruvada
2018-05-16 7:22 ` Peter Zijlstra
2018-05-16 9:15 ` Rafael J. Wysocki
2018-05-16 10:43 ` Peter Zijlstra
2018-05-16 15:39 ` Srinivas Pandruvada
2018-05-16 15:41 ` Srinivas Pandruvada
2018-05-16 4:49 ` [RFC/RFT] [PATCH 04/10] cpufreq: intel_pstate: Add update_util_hook for HWP Srinivas Pandruvada
2018-05-16 4:49 ` [RFC/RFT] [PATCH 05/10] cpufreq: intel_pstate: HWP boost performance on IO Wake Srinivas Pandruvada
2018-05-16 7:37 ` Peter Zijlstra
2018-05-16 17:55 ` Srinivas Pandruvada
2018-05-17 8:19 ` Peter Zijlstra
2018-05-16 9:45 ` Rafael J. Wysocki
2018-05-16 19:28 ` Srinivas Pandruvada
2018-05-16 4:49 ` [RFC/RFT] [PATCH 06/10] cpufreq / sched: Add interface to get utilization values Srinivas Pandruvada
2018-05-16 6:40 ` Viresh Kumar
2018-05-16 22:25 ` Srinivas Pandruvada
2018-05-16 8:11 ` Peter Zijlstra
2018-05-16 22:40 ` Srinivas Pandruvada
2018-05-17 7:50 ` Peter Zijlstra
2018-05-16 4:49 ` [RFC/RFT] [PATCH 07/10] cpufreq: intel_pstate: HWP boost performance on busy task migrate Srinivas Pandruvada
2018-05-16 9:49 ` Rafael J. Wysocki
2018-05-16 20:59 ` Srinivas Pandruvada
2018-05-16 4:49 ` [RFC/RFT] [PATCH 08/10] cpufreq: intel_pstate: Dyanmically update busy pct Srinivas Pandruvada
2018-05-16 7:43 ` Peter Zijlstra
2018-05-16 7:47 ` Peter Zijlstra
2018-05-16 4:49 ` [RFC/RFT] [PATCH 09/10] cpufreq: intel_pstate: New sysfs entry to control HWP boost Srinivas Pandruvada
2018-05-16 4:49 ` [RFC/RFT] [PATCH 10/10] cpufreq: intel_pstate: enable boost for SKX Srinivas Pandruvada
2018-05-16 7:49 ` Peter Zijlstra
2018-05-16 15:46 ` Srinivas Pandruvada
2018-05-16 15:54 ` Peter Zijlstra
2018-05-17 0:52 ` Srinivas Pandruvada
2018-05-16 6:49 ` [RFC/RFT] [PATCH 00/10] Intel_pstate: HWP Dynamic performance boost Juri Lelli
2018-05-16 15:43 ` Srinivas Pandruvada
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