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: Fri, 18 May 2018 14:33:53 +0100 [thread overview]
Message-ID: <20180518133353.GO30654@e110439-lin> (raw)
In-Reply-To: <20180518112919.GI12217@hirez.programming.kicks-ass.net>
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
next prev parent reply other threads:[~2018-05-18 13:34 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 [this message]
2018-05-30 16:57 ` Patrick Bellasi
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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