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Posts tagged with 'thermal'

Colin Ian King

Over the past month I've been hitting excessive thermal heating on my laptop and kidle_inject has been kicking in to try and stop the CPU from overheating (melting!).  A quick double-check with older kernels showed me that this issue was not thermal/performance regression caused by software - instead it was time to clean my laptop and renew the thermal paste.

After some quick research, I found that Artic MX-4 Thermal Compound provided an excellent thermal conductivity rating of 8.5W/mK so I ordered a 4g sample as well as a can of pressurized gas cleaner to clean out dust.

The X230 has an excellent hardware maintenance manual, and following the instructions I stripped the laptop right down so I could pop the heat pipe contacts off the CPU and GPU.  I carefully cleaned off the old dry and cracked thermal paste and applied about 0.2g of MX-4 thermal compound to the CPU and GPU and re-seated the heat pipe.  With the pressurized gas I cleaned out the fan and airways to maximize airflow over the heatpipe.   The entire procedure took about an hour to complete and for once I didn't have any screws left over after re-assembly!

I normally take photos of the position of components during the strip down of a laptop for reference in case I cannot figure out exactly how parts are meant to fix on the re-assembly phase.  In this case, the X230 maintenance manual is sufficiently detailed so I didn't take any photos this time.

I'm glad to report that my X230 is now no-longer overheating. Heat is being effectively pumped away from the CPU and GPU and one can feel the additional heat being pushed out of the laptop.  Once again I can fully max out the CPU and GPU without passive thermal cooling mechanisms being kicked into action, so I've now got 100% of my CPU performance back again; as good as new!

Now and again I see laptop overheating bugs being filed in LaunchPad.  While some are legitimate issues with broken software, I do wonder if the majority of issues with the older laptops is simply due to accumulation of dust and/or old and damaged thermal paste.

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Colin Ian King

Powerstat and thermal zones

Last night I was mulling over an overheating laptop issue that was reported by a user that turned out to be fluff and dust clogging up the fan rather than the intel_pstate driver being broken.

While it is a relief that the kernel driver is not at fault, it still bothered me that this kind of issue should be very simple to diagnose but I overlooked the obvious.   When solving these issues it is very easy to doubt that the complex part of a system is working correctly (e.g. a kernel driver) rather than the simpler part (e.g. the fan not working efficiently).  Normally, I try to apply Occam's Razor which in the simplest form can be phrased as:

"when you have two competing theories that make exactly the same predictions, the simpler one is the better."

..e.g. in this case, the fan is clogged up.

Fortunately, laptops invariably provide Thermal Zone information that can be monitored and hence one can correlate CPU activity with the temperature of various components of a laptop.  So last night I added Thermal Zone sampling to powerstat 0.02.00 which is enabled with the new -t option.

 
powerstat -tfR 0.5
Running for 60.0 seconds (120 samples at 0.5 second intervals).
Power measurements will start in 0 seconds time.

Time User Nice Sys Idle IO Run Ctxt/s IRQ/s Watts x86_pk acpitz CPU Freq
11:13:15 5.1 0.0 2.1 92.8 0.0 1 7902 1152 7.97 62.00 63.00 1.93 GHz
11:13:16 3.9 0.0 2.5 93.1 0.5 1 7168 960 7.64 63.00 63.00 2.73 GHz
11:13:16 1.0 0.0 2.0 96.9 0.0 1 7014 950 7.20 63.00 63.00 2.61 GHz
11:13:17 2.0 0.0 3.0 94.5 0.5 1 6950 960 6.76 64.00 63.00 2.60 GHz
11:13:17 3.0 0.0 3.0 93.9 0.0 1 6738 994 6.21 63.00 63.00 1.68 GHz
11:13:18 3.5 0.0 2.5 93.6 0.5 1 6976 948 7.08 64.00 63.00 2.29 GHz
.... 

..the -t option now shows x86_pk (x86 CPU package temperature) and acpitz (APCI thermal zone) temperature readings in degrees Celsius.

Now this is where the fun begins.  I ran powerstat for 60 seconds at 2 samples per second and then imported the data into LibreOffice.  To easily show corrleations between CPU load, power consumption, temperature and CPU frequency I normalized the data so that the lowest values were 0.0 and the highest were 1.0 and produced the following graph:

One can see that the CPU frequency (green) scales with the the CPU load (blue) and so does the CPU power (orange).   CPU temperature (yellow) jumps up quickly when the CPU is loaded and then steadily increases.  Meanwhile, the ACPI thermal zone (purple) trails the CPU load because it takes time for the machine to warm up and then cool down (it takes time for a fan to pump out the heat from the machine).

So, next time a laptop runs hot, running powerstat will capture the activity and correlating temperature with CPU activity should allow one to see if the overheating is related to a real CPU frequency scaling issue or a clogged up fan (or broken heat pipe!).

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Colin Ian King

even more stress in stress-ng

Over the past few weeks in spare moments I've been adding more stress methods to stress-ng  ready for Ubuntu 15.04 Vivid Vervet.   My intention is to produce a rich set of stress methods that can stress and exercise many facets of a system to force out bugs, catch thermal over-runs and generally torture a kernel in a controlled repeatable manner.

I've also re-structured the tool in several ways to enhance the features and make it easier to maintain.  The cpu stress method has been re-worked to include nearly 40 different ways to stress a processor, covering:

  • Bit manipulation: bitops, crc16, hamming
  • Integer operations: int8, int16, int32, int64, rand
  • Floating point:  long double, double,  float, ln2, hyperbolic, trig
  • Recursion: ackermann, hanoi
  • Computation: correlate, euler, explog, fibonacci, gcd, gray, idct, matrixprod, nsqrt, omega, phi, prime, psi, rgb, sieve, sqrt, zeta
  • Hashing: jenkin, pjw
  • Control flow: jmp, loop
..the intention was to have a wide enough eclectic mix of CPU exercising tests that cover a wide range of typical operations found in computationally intense software.   Use the new --cpu-method option to select the specific CPU stressor, or --cpu-method all to exercise all of them sequentially.

I've also added more generic system stress methods too:
  • bigheap - re-allocs to force OOM killing
  • rename - rename files rapidly
  • utime - update file modification times to create lots of dirty file metadata
  • fstat - rapid fstat'ing of large quantities of files
  • qsort - sorting of large quantities of random data
  • msg - System V message sending/receiving
  • nice - rapid re-nicing processes
  • sigfpe - catch rapid division by zero errors using SIGFPE
  • rdrand - rapid reading of Intel random number generator using the rdrand instruction (Ivybridge and later CPUs only)
Other new options:
  • metrics-brief - this dumps out only the bogo-op metrics that are relevant for just the tests that were run.
  • verify - this will sanity check the stress results per iteration to ensure memory operations and CPU computations are working as expected. Hopefully this will catch any errors on a hot machine that has errors in the hardware. 
  • sequential - this will run all the stress methods one by one (for a default of 60 seconds each) rather than all in parallel.   Use this with the --timeout option to run all the stress methods sequentially each for a specified amount of time. 
  • Specifying 0 instances of any stress method will run an instance of the stress method on all online CPUs. 
The tool also builds and runs on Debian kFreeBSD and GNU HURD kernels although some stress methods or stress options are not included due to lack of support on these other kernels.
The stress-ng man page gives far more explanation of each stress method and more detailed examples of how to use the tool.

For more details, visit here or read the manual.

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Colin Ian King

Keeping cool with thermald

The push for higher performance desktops and laptops has inevitably lead to higher power dissipation.  Laptops have also shrunk in size leading to increasing problems with removing excess heat and thermal overrun on heavily loaded high end machines.

Intel's thermald prevents machines from overheating and has been recently introduced in the Ubuntu Trusty 14.04 LTS release.  Thermald actively monitors thermal sensors and will attempt to keep the hardware cool by modifying a variety of cooling controls:
 

* Active or passive cooling devices as presented in sysfs
* The Running Average Power Limit (RAPL) driver (Sandybridge upwards)
* The Intel P-state CPU frequency driver (Sandybridge upwards)
* The Intel PowerClamp driver

Thermald has been found to be especially useful when using the Intel P-state CPU frequency scaling driver since this can push the CPU harder than other CPU frequency scaling drivers.

Over the past several weeks I've been working with Intel to shake out some final bugs and get thermald included into Ubuntu 14.04 LTS, so kudos to Srinivas Pandruvada for handling my patches and also providing a lot of timely fixes too.

By default, thermald works without any need for configuration, however, if one has incorrect thermal trip settings or other firmware related thermal zone bugs one can write one's own thermald configuration. 

For further details, consult the Ubuntu thermald wiki page.

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