From: Andreas Herrmann <aherrmann@suse.com>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Frederic Weisbecker <frederic@kernel.org>,
Viresh Kumar <viresh.kumar@linaro.org>,
Linux PM <linux-pm@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Commit 554c8aa8ecad causing severe performance degression with pcc-cpufreq
Date: Tue, 17 Jul 2018 12:21:36 +0200 [thread overview]
Message-ID: <20180717102136.snayvzmv2h3dcwiq@suselix> (raw)
In-Reply-To: <3724084.DyflrVPzDS@aspire.rjw.lan>
On Tue, Jul 17, 2018 at 12:09:21PM +0200, Rafael J. Wysocki wrote:
> On Tuesday, July 17, 2018 11:36:20 AM CEST Andreas Herrmann wrote:
> > On Tue, Jul 17, 2018 at 11:27:21AM +0200, Andreas Herrmann wrote:
> > > On Tue, Jul 17, 2018 at 11:23:25AM +0200, Rafael J. Wysocki wrote:
> > > > On Tue, Jul 17, 2018 at 11:11 AM, Andreas Herrmann <aherrmann@suse.com> wrote:
> > > > > On Tue, Jul 17, 2018 at 11:06:29AM +0200, Rafael J. Wysocki wrote:
> > > > >> On Tue, Jul 17, 2018 at 10:50 AM, Andreas Herrmann <aherrmann@suse.com> wrote:
> > > > >>
> > > > >> [cut]
> > > > >>
> > > > >> >
> > > > >> > On balance before this commit users could use pcc-cpufreq but had
> > > > >> > already suboptimal performance (compared to say intel_pstate driver
> > > > >> > which can be used changing BIOS options).
> > > > >>
> > > > >> BTW, I wonder why you need to change the BIOS options for intel_pstate to load.
> > > > >
> > > > > I think this is because of (in intel_pstate_init()):
> > > > >
> > > > > /*
> > > > > * The Intel pstate driver will be ignored if the platform
> > > > > * firmware has its own power management modes.
> > > > > */
> > > > > if (intel_pstate_platform_pwr_mgmt_exists())
> > > > > return -ENODEV;
> > > > >
> > > >
> > > > OK, because of the "Proliant" entry, right?
> > > >
> > > > So it looks like we have an issue there. We find the entry and we
> > > > look for _PSS. It is not there, so we assume that the firmware is
> > > > expected to control performance, which is not the case.
> >
> > FYI, there is another BIOS setting on those systems. It's called
> > "Collaborative Power Control" (AFAIK enabled by default).
> >
> > Only if this is disabled, firmware is (alone) in control of
> > performance. (And of course in this case neither pcc-cpufreq nor
> > intel_pstate will be loaded).
>
> OK, the patch is below.
>
> First, I hope that if "Collaborative Power Control" is disabled, it will
> simply hide the PCCH object and so intel_pstate will still not load then.
PCCH is hidden in that case.
> The main question basically is what the OS is expected to do if
> "Dynamic Power Savings Mode" is set. If we are *expected* to use
> the PCC interface then, intel_pstate may not work in that case, but
> I suspect that the PCC interface allows extra energy to be saved
> over what is possible without it.
I'll test it and see what happens.
Andreas
> ---
> drivers/cpufreq/intel_pstate.c | 17 ++++++++++++++++-
> 1 file changed, 16 insertions(+), 1 deletion(-)
>
> Index: linux-pm/drivers/cpufreq/intel_pstate.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/intel_pstate.c
> +++ linux-pm/drivers/cpufreq/intel_pstate.c
> @@ -2391,6 +2391,18 @@ static bool __init intel_pstate_no_acpi_
> return true;
> }
>
> +static bool __init intel_pstate_no_acpi_pcch(void)
> +{
> + acpi_status status;
> + acpi_handle handle;
> +
> + status = acpi_get_handle(NULL, "\\_SB", &handle);
> + if (ACPI_FAILURE(status))
> + return true;
> +
> + return !acpi_has_method(handle, "PCCH");
> +}
> +
> static bool __init intel_pstate_has_acpi_ppc(void)
> {
> int i;
> @@ -2450,7 +2462,10 @@ static bool __init intel_pstate_platform
>
> switch (plat_info[idx].data) {
> case PSS:
> - return intel_pstate_no_acpi_pss();
> + if (!intel_pstate_no_acpi_pss())
> + return false;
> +
> + return intel_pstate_no_acpi_pcch();
> case PPC:
> return intel_pstate_has_acpi_ppc() && !force_load;
> }
>
>
next prev parent reply other threads:[~2018-07-17 10:22 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-17 6:50 Commit 554c8aa8ecad causing severe performance degression with pcc-cpufreq Andreas Herrmann
2018-07-17 7:33 ` Rafael J. Wysocki
2018-07-17 8:03 ` Rafael J. Wysocki
2018-07-17 8:50 ` Andreas Herrmann
2018-07-17 8:58 ` Rafael J. Wysocki
2018-07-17 9:06 ` Rafael J. Wysocki
2018-07-17 9:11 ` Andreas Herrmann
2018-07-17 9:23 ` Rafael J. Wysocki
2018-07-17 9:27 ` Andreas Herrmann
2018-07-17 9:36 ` Andreas Herrmann
2018-07-17 10:09 ` Rafael J. Wysocki
2018-07-17 10:21 ` Andreas Herrmann [this message]
2018-07-17 10:23 ` Rafael J. Wysocki
2018-07-17 14:03 ` Andreas Herrmann
2018-07-17 15:29 ` Rafael J. Wysocki
2018-07-17 16:13 ` [PATCH] cpufreq: intel_pstate: Load when ACPI PCCH is present Rafael J. Wysocki
2018-07-17 17:23 ` Srinivas Pandruvada
2018-07-17 17:28 ` Rafael J. Wysocki
2018-07-17 18:06 ` [PATCH] cpufreq: intel_pstate: Register " Rafael J. Wysocki
2018-07-18 10:43 ` Andreas Herrmann
2018-07-18 10:51 ` Rafael J. Wysocki
2018-07-17 10:18 ` Commit 554c8aa8ecad causing severe performance degression with pcc-cpufreq Andreas Herrmann
2018-07-17 8:08 ` Daniel Lezcano
2018-07-17 8:36 ` Andreas Herrmann
2018-07-17 8:52 ` Rafael J. Wysocki
2018-07-17 8:15 ` Peter Zijlstra
2018-07-17 9:05 ` Andreas Herrmann
2018-07-17 12:02 ` [PATCH] cpufreq: pcc-cpufreq: Disable dynamic scaling on many-CPU systems Rafael J. Wysocki
2018-07-17 16:14 ` [PATCH v2] " Rafael J. Wysocki
2018-07-17 20:13 ` Andreas Herrmann
2018-07-18 7:44 ` Rafael J. Wysocki
2018-07-18 8:23 ` Peter Zijlstra
2018-07-18 9:34 ` Andreas Herrmann
2018-07-18 15:25 ` Commit 554c8aa8ecad causing severe performance degression with pcc-cpufreq Andreas Herrmann
2018-07-18 15:31 ` Andreas Herrmann
2018-07-19 11:04 ` Andreas Herrmann
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