New: Intel Pstate driver minimum percent does not change with turbo off
https://bugzilla.kernel.org/show_bug.cgi?id=64251
Bug ID: 64251
Summary: Intel Pstate driver minimum percent does not change
with turbo off
Product: Power Management
Version: 2.5
Kernel Version: 3.12rc7
Hardware: All
OS: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: cpufreq
Assignee: [email protected]
Reporter: [email protected]
Regression: No
Created attachment 113141
--> https://bugzilla.kernel.org/attachment.cgi?id=113141&action=edit
Frequency Vs. Requested Frequency
When turbo is turned off the maximum frequency percent does not change. O.K. So the minimum frequency percent should change, but it doesn't.
Using my computer as an example: The turbo on maximum frequency is 3.8 GHz; The turbo off maximum frequency is 3.4 GHz; The minimum frequency is 1.6 GHz.
Therefore we would expect: For turbo on, max percent = 100, min percent = 42; For turbo off, max percent = 100, min percent = 47.
starting from a fresh boot:
doug@s15:~$ uname -a Linux s15 3.12.0-rc7+ #48 SMP Fri Nov 1 21:09:51 PDT 2013 x86_64 x86_64 x86_64 GNU/Linux doug@s15:~$ cat /sys/devices/system/cpu/intel_pstate/* 100 42 0 doug@s15:~$ cd temp doug@s15:~/temp$ sudo ./set_cpu_turbo_off [sudo] password for doug: doug@s15:~/temp$ cat /sys/devices/system/cpu/intel_pstate/* 100 42 1 doug@s15:~/temp$ cat set_cpu_turbo_off #! /bin/bash echo "1" > /sys/devices/system/cpu/intel_pstate/no_turbo
The attached png file demonstrates. (the rounding part will be a separate bug report)
Note: This bug is extracted from bug 59481 which mentioned several issues, the main issue was solved and the bug closed. Now I am following up on the other issues.
Signature · 2 lines
You are receiving this mail because: You are the assignee for the bug.
[Bug 64251] Intel Pstate driver minimum percent does not change with turbo off
https://bugzilla.kernel.org/show_bug.cgi?id=64251
Dirk Brandewie <[email protected]> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |[email protected]
--- Comment #1 from Dirk Brandewie <[email protected]> --- min_pct_perf is a user configurable floor value (not to go below) so it is still valid in both cases.
Signature · 2 lines
You are receiving this mail because: You are the assignee for the bug.
[Bug 64251] Intel Pstate driver minimum percent does not change with turbo off
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=64251
--- Comment #2 from Doug Smythies <[email protected]> ---
But the system overrides any user value that had been previously set upon mode change. It doesn't make any sense (to me at least) in turbo off that it be set to 42, which is basically a meaningless number under these conditions.
Example:
doug@s15:~/temp$ echo "53" | sudo tee /sys/devices/system/cpu/intel_pstate/min_perf_pct 53 doug@s15:~/temp$ cat /sys/devices/system/cpu/intel_pstate/* 53 53 1 doug@s15:~/temp$ sudo ./set_cpu_performance doug@s15:~/temp$ cat /sys/devices/system/cpu/intel_pstate/* 100 100 0 doug@s15:~/temp$ sudo ./set_cpu_powersave doug@s15:~/temp$ cat /sys/devices/system/cpu/intel_pstate/* 53 42 0
Signature · 2 lines
You are receiving this mail because: You are the assignee for the bug.
[Bug 64251] Intel Pstate driver minimum percent does not change with turbo off
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=64251
--- Comment #3 from Dirk Brandewie <[email protected]> --- I was trying to provide some useful information by setting min_perf_pct to a value. I guess I could leave it at 0 since any value between 0 and the percent of the cpu represented by the lowest P state are the same.
The reason for having the ability to disable turbo is for people that avoid the possible jitter introduced into the system caused by thermal throttling.
If you want to limit the P state selection to something to something greater than the minimum to further reduce jitter caused by P state transitions then you would set the min/floor value to something significantly higher than the minimums.
Regardless 42% is a valid floor value.
Signature · 2 lines
You are receiving this mail because: You are the assignee for the bug.
[Bug 64251] Intel Pstate driver minimum percent does not change with turbo off
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=64251
--- Comment #4 from Doug Smythies <[email protected]> --- (In reply to Dirk Brandewie from comment #3)
Quoted 2 lines
I was trying to provide some useful information by setting
min_perf_pctto a value.
Which I totally agree with, and do find the information very useful. I am just suggesting that it would be equally useful to provide that same information for the other cases.
I see 4 scenarios, maybe there are more (using my computer as the example):
1.) BIOS allows Turbo mode and Turbo on enabled in driver:
min = 42 percent, which represents 1.6 GHz and is accurate max = 100 percent, which represents 3.8 GHz and is accurate
2.) BIOS allows Turbo mode and Turbo is disabled in driver:
min = 42 percent, which doesn't represent anything. max = 100 percent, which represents 3.4 GHz and is accurate.
3.) BIOS disabled Turbo mode and Turbo on enabled in driver:
min = 42 percent, which represents 1.6 GHz and is accurate. max = 100 percent, which represents 3.8 GHz, but can not be achieved. (a supporting graph will be attached in a minute)
4.) BIOS disabled Turbo mode and Turbo is disabled in driver:
This does not work at all on my computer. The CPU frequency just locks at whatever it was when the driver Turbo disable transition command is issued. (a supporting graph will be attached in a minute)
Signature · 2 lines
You are receiving this mail because: You are the assignee for the bug.
[Bug 64251] Intel Pstate driver minimum percent does not change with turbo off
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=64251
--- Comment #5 from Doug Smythies <[email protected]> --- Created attachment 113721
--> https://bugzilla.kernel.org/attachment.cgi?id=113721&action=edit
BIOS disabled Turbo mode CPU freq Vs. Requested.
This graph is in support of the previous comments.
The "rnd" and "nokick" in the legend are related to other bug reports, and can be ignored in the context of this bug report. They are both with driver turbo on, but BIOS turbo disabled.
"Toff" means driver turbo disabled, and multiple tests were done, each one with a different frequency on CPU 7 at the time of driver transition from turbo enabled to disabled, to demonstrate that the CPU frequency will lock and be thereafter unchangeable.
Signature · 2 lines
You are receiving this mail because: You are the assignee for the bug.
[Bug 64251] Intel Pstate driver minimum percent does not change with turbo off
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=64251
Lan Tianyu <[email protected]> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |[email protected] Assignee|[email protected] |[email protected]
Signature · 2 lines
You are receiving this mail because: You are the assignee for the bug.