[Bug 173361] New: Under heavy load, the CPU speed suddenly and irreversibly drops from 3500 to 400 MHz

[Bug 173361] New: Under heavy load, the CPU speed suddenly and irreversibly drops from 3500 to 400 MHz

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=173361

            Bug ID: 173361
           Summary: Under heavy load, the CPU speed suddenly and
                    irreversibly drops from 3500 to 400 MHz
           Product: Power Management
           Version: 2.5
    Kernel Version: 4.8-rc1
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: cpufreq
          Assignee: linux-pm@vger.kernel.org
          Reporter: Larry.Finger@lwfinger.net
        Regression: No

My Toshiba Tecra A50-A laptop that a CPU described as 'Model: 6.60.3 "Intel(R)
Core(TM) i7-4600M CPU @ 2.90GHz"'. Under heavy load, this dual-core unit with
hyperthreading will suddenly drop from a frequency of 3500 to 410 MHz. The only
way to recover is to reboot. See
http://lkml.iu.edu/hypermail/linux/kernel/1609.3/00720.html for some details
and other discussion.

This bug is being filed under power management because the 'sensors' command
shows the following:

finger@linux-1t8h:~> sensors
coretemp-isa-0000
Adapter: ISA adapter
Physical id 0:  +88.0°C  (high = +84.0°C, crit = +100.0°C)
Core 0:         +88.0°C  (high = +84.0°C, crit = +100.0°C)
Core 1:         +77.0°C  (high = +84.0°C, crit = +100.0°C)

Routinely, at least one of the CPUs has a temperature higher than the "high"
value. As Rafael Wysocki states "It looks like in 4.8-rc we made a change that
caused the "high" trip point to be acted on." In that case, the bug would be
that the frequency is never restored.

-- 
You are receiving this mail because:
You are the assignee for the bug.

[Bug 173361] Under heavy load, the CPU speed suddenly and irreversibly drops from 3500 to 400 MHz

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=173361

Doug Smythies <dsmythies@telus.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dsmythies@telus.net

--- Comment #1 from Doug Smythies <dsmythies@telus.net> ---
For what it is worth, some data from my computer:

. I get the exact same steady state temperature and package power under full
load with both kernel 4.7 and 4.8-rc8.

. I messed with the cooling so that it could exceed the high limit, and when it
did nothing tripped (as expected):

doug@s15:~/temp2$ sensors
coretemp-isa-0000
Adapter: ISA adapter
Physical id 0:  +81.0°C  (high = +80.0°C, crit = +98.0°C)
Core 0:         +77.0°C  (high = +80.0°C, crit = +98.0°C)
Core 1:         +81.0°C  (high = +80.0°C, crit = +98.0°C)
Core 2:         +77.0°C  (high = +80.0°C, crit = +98.0°C)
Core 3:         +78.0°C  (high = +80.0°C, crit = +98.0°C)

For this comment from the e-mail thread: "Hmm, I would not expect the CPU to
drop from 80 to 40 degrees in a few seconds if the fan is not spinning.  I
wouldn't even expect it if the fan was spinning.  I would think at least 30 to
60 seconds if not more."

I from a steady state, full load, temperature of 78 degrees C to 0 load I see:
15 degrees drop in 1 second; 18 degrees drop in 2 seconds; 22 degrees drop in
10 seconds; 25 degrees droop in 20 seconds.

For the original post comment: "In that case, the bug would be that the
frequency is never restored."
It isn't supposed to restore. I do not know why in this case it is kicking in
at 50%, usually it is less. Regardless, the current control algorithm in the
intel_pstate driver is fundamentally incompatible with clock modulation, and
will always drive the CPU down to the minimum * the modulation %, regardless of
load. Other drivers typically drive the CPU frequency to what would normally be
desired * modulation % (and for the most part users don't even notice).

-- 
You are receiving this mail because:
You are the assignee for the bug.

[Bug 173361] Under heavy load, the CPU speed suddenly and irreversibly drops from 3500 to 400 MHz

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=173361

--- Comment #2 from Larry Finger <Larry.Finger@lwfinger.net> ---
I have not measured the drop in temperature with change in load, but I know it
happens very quickly, and that the fan speed is very sensitive to the load.
Even when running 4 infinite loops, sending a E-mail with Thunderbird will
decrease the CPU utilization enough that the fan will momentarily slow.

-- 
You are receiving this mail because:
You are the assignee for the bug.

[Bug 173361] Under heavy load, the CPU speed suddenly and irreversibly drops from 3500 to 400 MHz

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=173361

--- Comment #3 from Doug Smythies <dsmythies@telus.net> ---
Created attachment 240221
  --> https://bugzilla.kernel.org/attachment.cgi?id=240221&action=edit
Script to continuously monitor package temperature

I guess the point is that one can not come after the event trigger and obtain
anything close to related temperatures. Perhaps the attached script could be
used to monitor package temperature from well before to well after the event.

-- 
You are receiving this mail because:
You are the assignee for the bug.

[Bug 173361] Under heavy load, the CPU speed suddenly and irreversibly drops from 3500 to 400 MHz

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=173361

--- Comment #4 from Larry Finger <Larry.Finger@lwfinger.net> ---
Thanks. I'm running the script with the continuing test of 4.7, which has been
running for a little over 30 hours without triggering the event.

-- 
You are receiving this mail because:
You are the assignee for the bug.

[Bug 173361] Under heavy load, the CPU speed suddenly and irreversibly drops from 3500 to 400 MHz

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=173361

Rafael J. Wysocki <rjw@rjwysocki.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rjw@rjwysocki.net
           Assignee|linux-pm@vger.kernel.org    |rjw@rjwysocki.net

-- 
You are receiving this mail because:
You are the assignee for the bug.