New: Intel P-State: Constantly changing CPU frequencies on idle system.
https://bugzilla.kernel.org/show_bug.cgi?id=77771
Bug ID: 77771
Summary: Intel P-State: Constantly changing CPU frequencies on
idle system.
Product: Power Management
Version: 2.5
Kernel Version: 3.14.7, 3.15-rc8 - 3.15
Hardware: x86-64
OS: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: cpufreq
Assignee: [email protected]
Reporter: [email protected]
Regression: NoWith the introduction of the kernel patch 3.14.7 and around the release of 3.15-rc8 the idle CPU frequency of each core in an idle system is changing erratically.
Before the patch the output of grep MHz /proc/cpuinfo looked like this:
cpu MHz : 813.625
cpu MHz : 813.625
cpu MHz : 813.625
cpu MHz : 813.625
After the patch:
cpu MHz : 1600.207
cpu MHz : 1600.207
cpu MHz : 1599.847
cpu MHz : 2342.675
The CPU clocks are wildly changing over the complete spectrum of available frequencies. I can reproduce the phenomenon on at least three systems:
Desktop PC with Sandy-Bridge CPU: Intel i7-2600 (non-K) Lenovo T530 with Ivy-Bridge CPU: i7-3610QM
Sony VAIO Pro 13 (example above) with Haswell CPU: i5-4200U
For me it is not clear whether this is expected behavior and I just hit some kind of heisenbug or something is going wrong. Primarily I report this because I noticed a significant sudden change. I haven't done any tests regarding performance, battery run-time or heat implications yet.
Note: I've seen this kind of behavior in earlier kernel releases before, but with 3.14 it vanished completely. So this might be a regression.
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[Bug 77771] Intel P-State: Constantly changing CPU frequencies on idle system.
https://bugzilla.kernel.org/show_bug.cgi?id=77771
Doug Smythies <[email protected]> changed:
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CC| |[email protected]
--- Comment #1 from Doug Smythies <[email protected]> --- Please define "an idle system". I ask because an "idle" linux server computer can be quite different than and "idle" linux computer with some sort of gui desktop, the latter being, in reality, actually considerably less "idle".
That being said, your frequencies do seem a little high now. Your previous frequencies were unduly being forced low and there was a change with respect to that issue.
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[Bug 77771] Intel P-State: Constantly changing CPU frequencies on idle system.
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=77771
Yuyang Du <[email protected]> changed:
What |Removed |Added
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CC| |[email protected]
--- Comment #2 from Yuyang Du <[email protected]> --- (In reply to Michael Long from comment #0)
Quoted 4 lines
With the introduction of the kernel patch 3.14.7 and around the release of 3.15-rc8 the idle CPU frequency of each core in an idle system is changing erratically.
This behavior is expected, see:
http://marc.info/?l=linux-pm&m=140141648726863&w=2
Nothing to say more.
Thanks,
Yuyang
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[Bug 77771] Intel P-State: Constantly changing CPU frequencies on idle system.
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=77771
--- Comment #3 from Michael Long <[email protected]> --- To comment #1:
I made my tests on desktop systems with a loaded KDE instance. Aside from "the usual" services running like in a typical Fedora 20 default installation. There are no other process active producing considerable load over a longer time.
I just started up, logged into KDE and let is stay for a while (at least 5 mins) and then looked at the frequencies. No browser started, no games loaded, no update-processes running etc, just an empty desktop.
There is nothing up and running on those systems that justifies having one or more cores up even deep in some turbo mode when getting the frequency stats.
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[Bug 77771] Intel P-State: Constantly changing CPU frequencies on idle system.
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=77771
--- Comment #4 from Doug Smythies <[email protected]> --- Created attachment 139771
--> https://bugzilla.kernel.org/attachment.cgi?id=139771&action=edit
turbostat look at idle system
Perhaps provide the output from "turbostat sleep 60" or "turbostat -J sleep 60".
I have attached the result from my system, where my CPU's are all at low frequency (lowest pstate). My system is a server with no GUI stuff.
I did it as an attachment rather than in-line, so as to (hopefully) not mess up the formatting.
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[Bug 77771] Intel P-State: Constantly changing CPU frequencies on idle system.
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=77771
--- Comment #5 from Michael Long <[email protected]> ---
Thanks for the hint about the turbostat utility. Without starting a desktop environment I got similar stats, all frequencies are very close around the lowest state. Logged into KDE showed different results. Eventually I found the cause of those high clocks:
A superkaramba desktop-widget. This widget basically does a grep on /proc/cpuinfo and checks the load internally each second. Disabling this widget gets the clock down. The same behavior can be reproduced just by running "for i in {1..99}; do grep MHz /proc/cpuinfo; sleep 1; done".
Admittedley this might be a typical layer8-problem, however why is a simple grep every second pounding the CPU so hard that it remains in higher clocks, even in turbo mode? Especially when it didn't before the patch or just using plain old acpi-cpufreq. If this is still just expected behavior sorry for the unnecessary noise.
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[Bug 77771] Intel P-State: Constantly changing CPU frequencies on idle system.
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=77771
--- Comment #6 from Michael Long <[email protected]> --- Created attachment 140001
--> https://bugzilla.kernel.org/attachment.cgi?id=140001&action=edit
turbostat results while running simple grep
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[Bug 77771] Intel P-State: Constantly changing CPU frequencies on idle system.
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=77771
--- Comment #7 from Yuyang Du <[email protected]> --- (In reply to Michael Long from comment #5)
Quoted 10 lines
Thanks for the hint about the turbostat utility. Without starting a desktop environment I got similar stats, all frequencies are very close around the lowest state. Logged into KDE showed different results. Eventually I found the cause of those high clocks:
A superkaramba desktop-widget. This widget basically does a grep on
/proc/cpuinfoand checks the load internally each second. Disabling this widget gets the clock down. The same behavior can be reproduced just by running "for i in {1..99}; do grep MHz/proc/cpuinfo; sleep 1; done".
Quoted 5 lines
Admittedley this might be a typical layer8-problem, however why is a simple grep every second pounding the CPU so hard that it remains in higher clocks, even in turbo mode? Especially when it didn't before the patch or just using plain old acpi-cpufreq. If this is still just expected behavior sorry for the unnecessary noise.
Expected, but should not happen. So clearly something is wrong...
Yuyang
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[Bug 77771] Intel P-State: Constantly changing CPU frequencies on idle system.
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=77771
--- Comment #8 from Doug Smythies <[email protected]> --- Created attachment 140031
--> https://bugzilla.kernel.org/attachment.cgi?id=140031&action=edit
two turbostats runs with grep running
Is your turbostat listing for your Haswell computer? I.E. the one where the minimum CPU frequency is about 800 MHz?
I am unable to repeat your "for i in {1..99}; do grep MHz /proc/cpuinfo; sleep 1; done" results on my computer. I wish that I could. Attached are two turbostat runs done while that command was running (the 2nd one is probably of no use to anyone else). My minimum CPU frequency is about 1600 MHz.
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[Bug 77771] Intel P-State: Constantly changing CPU frequencies on idle system.
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=77771
--- Comment #9 from Michael Long <[email protected]> --- Created attachment 140441
--> https://bugzilla.kernel.org/attachment.cgi?id=140441&action=edit
Kernel config 3.15
Sorry for the delay, yes the turbostat results are all from the same Haswell i5-4200U with 800-1600 MHz (turbo 2.9 GHz) [1].
I've no clue why this ultrabook is so sensitive. Hence I've attached my current kernel-config maybe I've misconfigured something.
In the meantime I tried to find a better method to reproduce the effect but I had no real luck when testing on my other quad-core systems. There, the effect is very less severe.
[1]
http://ark.intel.com/products/75459/Intel-Core-i5-4200U-Processor-3M-Cache-up-to-2_60-GHz?q=i5-4200U
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[Bug 77771] Intel P-State: Constantly changing CPU frequencies on idle system.
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=77771
Dirk Brandewie <[email protected]> changed:
What |Removed |Added
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--- Comment #10 from Dirk Brandewie <[email protected]> --- Can run "powertop --html sleep 30" and attach powertop.html
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[Bug 77771] Intel P-State: Constantly changing CPU frequencies on idle system.
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=77771
--- Comment #11 from Michael Long <[email protected]> --- Created attachment 140501
--> https://bugzilla.kernel.org/attachment.cgi?id=140501&action=edit
powertop report on idle system
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[Bug 77771] Intel P-State: Constantly changing CPU frequencies on idle system.
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=77771
--- Comment #12 from Michael Long <[email protected]> --- Created attachment 140511
--> https://bugzilla.kernel.org/attachment.cgi?id=140511&action=edit
powertop report with a grep in a loop
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[Bug 77771] Intel P-State: Constantly changing CPU frequencies on idle system.
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=77771
Lan Tianyu <[email protected]> changed:
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CC| |[email protected] Assignee|[email protected] |[email protected]
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