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From: Peter Zijlstra <peterz@infradead.org>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: 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: Thu, 17 May 2018 20:28:03 +0200	[thread overview]
Message-ID: <20180517182803.GY12217@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAJZ5v0j82sm94iCpLOVMBwoSksKx1Y49RfJv=nhhJiKhenZykg@mail.gmail.com>

On Thu, May 17, 2018 at 06:56:37PM +0200, Rafael J. Wysocki wrote:
> On Thu, May 17, 2018 at 6:42 PM, Srinivas Pandruvada

> > What will happen if we look at all core turbo as max and cap any
> > utilization above this to 1024?
> 
> I was going to suggest that.

To the basic premise behind all our frequency scaling is that there's a
linear relation between utilization and frequency, where u=1 gets us the
fastest.

Now, we all know this is fairly crude, but it is what we work with.

OTOH, the whole premise of turbo is that you don't in fact know what the
fastest is, and in that respect setting u=1 at the guaranteed or
sustainable frequency makes sense.

The direct concequence of allowing clipping is that u=1 doesn't select
the highest frequency, but since we don't select anything anyway
(p-code does that for us) all we really need is to have u=1 above that
turbo activation point you mentioned.

For parts where we have to directly select frequency this obviously
comes apart.

However; what happens when the sustainable freq drops below our initial
'max'? Imagine us dropping below the all-core-turbo because of AVX. Then
we're back to running at u<1 at full tilt.

Or for mobile parts, the sustainable frequency could drop because of
severe thermal limits. Now I _think_ we have the possibility for getting
interrupts and reading the new guaranteed frequency, so we could
re-guage.

So in theory I think it works, in practise we need to always be able to
find the actual max -- be it all-core turbo, AVX or thermal constrained
frequency. Can we do that in all cases?


I need to go back to see what the complains against Vincent's proposal
were, because I really liked the fact that it did away with all this.

  reply	other threads:[~2018-05-17 18:28 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 [this message]
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
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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