Re: [PATCH 0/4] thermal threshold event notification

[Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>]

Rafael, Len, Rui and Arjan,

Do you have any suggestions?



On 04/08/2013 08:26 AM, Guenter Roeck wrote:
> On Sun, Apr 07, 2013 at 07:40:08PM -0700, Srinivas Pandruvada wrote:
>> Hi Guenter,
>>
>> Thanks for your quick response. Please see my answers in-line.
>>
>> Thanks,
>> Srinivas
>>
>> On 04/05/2013 08:24 PM, Guenter Roeck wrote:
>>> On Thu, Apr 04, 2013 at 01:09:20PM -0700, Srinivas Pandruvada wrote:
>>>> On 04/04/2013 12:43 PM, Guenter Roeck wrote:
>>>>> On Thu, Apr 04, 2013 at 12:11:25PM -0700, Srinivas Pandruvada wrote:
>>>>>> This is clear that there is reluctance in adding thresholds in coretemp sysfs,
>>>>>> during previous attempts. Proably because of lake of use cases.
>>>>>> But this time use case may be more compelling.
>>>>>>
>>>>>> We have many small form factor devices like ultrabooks, slate PCs in the market.
>>>>>> Unfortunately these devices reach maximum temperature with relatively less
>>>>>> workloads, causing BIOS to do thermal throttling. There are real performance
>>>>>> issues due to aggressive BIOS action to control thermals and also thermal breakdown
>>>>>> in some cases.
>>>>>>
>>>>>> Even the most expensive laptops, don't have correct ACPI thermal configuration,
>>>>>> so that kernel thermal driver can act. In some case even the trip point is higher
>>>>>> than critical temperature setting.
>>>>>>
>>>>>> Intel has developed several drivers, which can be used to cool the system very efficiently.
>>>>>> They include RAPL based cooling driver, Powerclamp driver and P state driver.
>>>>>> To utilize these cooling device a closed loop user mode program is required, which
>>>>>> will utilize these method and dynamically compensate for high CPU temperatures,
>>>>>> without relying on any configuration data.
>>>>>> One such solution is developed is "Linux thermal daemon". More details can be
>>>>>> obtained from
>>>>>> "https://github.com/01org/thermal_daemon/blob/master/ThermalDaemon_Introduction.pdf".
>>>>>> This daemon polls for cpu temperature and apply compensation once the CPU reach target
>>>>>> temperature.
>>>>>>
>>>>>> This polling can be mostly avoided, by getting notification for the temperature, where
>>>>>> it needs to wake up and get ready for apply compensation. In most of the normal use
>>>>>> cases, there may not be any threshold events. So very minimal number of user space
>>>>>> notification for thermal thresholds.
>>>>>>
>>>>>> This patch adds two entries to coretemp sysfs.
>>>>>> tempX_notify_threshold_1
>>>>>> tempX_notify_threshold_2
>>>>>>
>>>>>> These two settings acts on "Package level", not on core level. So it will only appear
>>>>>> if there is support for package temperature. Many of recent Intel processors, support
>>>>>> package temperatures
>>>>>> When any valid value is written to these files, it will directly set corresponding CPU MSR,
>>>>>> in the corresponding package and read back directly from MSR. Since package MSR, affects
>>>>>> all cores in package, setting will be applicable to all CPU's in the package minimizing
>>>>>> read, writes and notifications. Also package threshold interrupts are enabled only when,
>>>>>> a non zero value is written to thresholds.
>>>>>>
>>>>>> Once thresholds are violated, it uses a rate control of 5 seconds, reducing the number
>>>>>> of interrupts, when temperature is hanging around trip point. Using the sticky log bit,
>>>>>> it sends kboject uevent change notification for corresponding package sysfs.
>>>>>> Once the thermal daemon receives notification, it can change to new threshold or act
>>>>>> immediately to reduce CPU temperature.
>>>>>>
>>>>>>
>>>>>> Srinivas Pandruvada (4):
>>>>>>    x86, mcheck, therm_throt: Process package thresholds
>>>>>>    hwmon: (coretemp) Add threshold support
>>>>>>    hwmon: (coretemp) : Add notification support
>>>>>>    drivers/hwmon/coretemp : Debug fs interface
>>>>>>
>>>>>>   arch/x86/include/asm/mce.h               |   7 +
>>>>>>   arch/x86/kernel/cpu/mcheck/therm_throt.c |  50 ++++-
>>>>>>   drivers/hwmon/coretemp.c                 | 319 +++++++++++++++++++++++++++++--
>>>>>>   3 files changed, 361 insertions(+), 15 deletions(-)
>>>>>>
>>>>> Key question: Why does the thermal subsystem not work for you ?
>>>> Thermal is bigger issue in Ultrabooks, Slate PCs and other small
>>>> form factor devices.
>>>> Linux ACPI thermal driver depends on ACPI configuration to activate
>>>> active/passive control. So if you have garbage data or not optimized
>>>> data, the current Linux driver can't control thermals. There are
>>>> multiple platforms with bad ACPI data. Some of them have "ACPI
>>>> threshold > critical temp"
>>>>
>>> I wasn't talking about ACPI, I was talking about the Linux thermal subsystem
>>> in drivers/thermal. There is no single mention of "ACPI" in that directory.
>> <Thermal drivers also  resides outside this directory. ACPI also
>> registers as thermal zone similar to other example you mentioned
>> below. ACPI is the only means to configure per platform thermal trip
>> points in thermal zones in PC platform.
>>>
>>>> Currently all these systems, rely on BIOS fan and T state control.
>>>> Once T states are used the performance gets hurt. Also we had cases
>>>> of thermal breakdown.
>>>>
>>>> In addition there are several new methods to cool the system,
>>>> developed by Intel and are in latest Linux kernel. They are
>>>> specially designed to cool the system when needed.
>>>>
>>> So, again, why can't you use the thermal subsystem ?
>> <Thermal zone needs to show temperature.  This will be duplicate
>> what coretemp.X is showing. I want to prevent identical information
>> be displayed at two different sysfs>
>> Also the db8500 example you are giving, uses a pre-configured
>> thresholds loaded during probe().
>> There is no thermal ABI to set thresholds at run time. Basically
>> when a temperature is above a trip temp, corresponding cooling
>> devices will be activated.
>> So I still I have to write a platform driver to set thresholds, and
>> then registers with thermal zone. This will show as another
>> packagetemp.x at sysfs like coretemp.x.
>>
>> So please let me know how to set dynamic thresholds?
>>> The db8500_thermal driver in drivers/thermal is quite similar to what
>>> you try to accomplish. I would suggest to look into it and use a similar
>>> approach. I really don't see how this fits into the hwmon subsystem.
>> <Is this logic based on that hwmon shouldn't have write interface
>> and used only for monitoring?  I think some hwmon driver already
>> have write interface like gpiofan.>
> That isn't the point. hwmon is static in nature, not dynamic. Its scope is
> hardware monitoring, not thermal management. This is what the thermal subsystem
> is for. Yes, presumably you would need a platform driver to set the thresholds.
> Another question, though, would be if you want or need a user space component in
> the first place or if you can implement all required functionality in a thermal
> driver.
>
> Copying Zhang Rui and the linux-pm mailing list to get feedback from others.

We have debated user vs kernel space. Both are required.
There are many thermal modelling algorithms can be designed in user 
space and it is already distributed by another OS to vendors. User space 
can learn and model system based on usage. Kernel can always act on well 
designed pre-configured or dynamically on request.
My coretemp patches are managing thermal, it is aiding in therma 
management as sensors.

Thanks,
Srinivas