[lm-sensors] Does this makes any sense?

[lm-sensors] Does this makes any sense?

[=?unknown-8bit?q?=C3=93scar?= Fuentes]

This is not a problem with lm-sensors, but an attempt to understand
what can cause the values it outputs.

When I start four mprime processes in "torture test" mode on a Q6600
system it shows a flat 100% CPU usage line and `sensors` report
temperatures around or below 70 degrees Celsius for each core, which
is consistent with Intel's specs for a fully loaded CPU:

oscar@qcore:~/Archivo/prime$ sensors
coretemp-isa-0000
Adapter: ISA adapter
Core 0:      +73.0°C  (crit = +100.0°C)

coretemp-isa-0001
Adapter: ISA adapter
Core 1:      +71.0°C  (crit = +100.0°C)

coretemp-isa-0002
Adapter: ISA adapter
Core 2:      +62.0°C  (crit = +100.0°C)

coretemp-isa-0003
Adapter: ISA adapter
Core 3:      +58.0°C  (crit = +100.0°C)

However, when compiling an application with "make -j 4" the CPU usage
is around 95% (which is expected as there is quite a bit of I/O
involved) but the temperature goes up to 88 degrees on some cores!
This is a typical output of `sensors` on this scenario:

coretemp-isa-0000                   
Adapter: ISA adapter                
Core 0:      +85.0°C  (crit = +100.0°C)

coretemp-isa-0001
Adapter: ISA adapter
Core 1:      +82.0°C  (crit = +100.0°C)

coretemp-isa-0002
Adapter: ISA adapter
Core 2:      +71.0°C  (crit = +100.0°C)

coretemp-isa-0003
Adapter: ISA adapter
Core 3:      +65.0°C  (crit = +100.0°C)

What can cause this difference on temperatures, when mprime stresses
the CPU much more than the compiler?

-- 
Oscar

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Re: [lm-sensors] Does this makes any sense?

[Rudolf Marek]

Hi,

Maybe the IO stresses the CPU more.

Rudolf

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Re: [lm-sensors] Does this makes any sense?

[Óscar Fuentes]

Rudolf Marek <r.marek@assembler.cz> writes:

> Maybe the IO stresses the CPU more.

mprime is FPU and memory intensive. The I/O for the compiler is
reading and writing on the disk, which means memory I/O, but nowhere as
intensive as mprime.

If the average of the temperature on the CPU cores is indicative of the
T_c (the temperature metrology spec used by Intel) while compiling the
CPU should be much above the temperature at maximum load, per Intel's
spec (71 degrees measured at the geometrical center of the CPU).

Another strange thing is the difference among cores. This seems to be
always true: Core0 Temp > Core1 Temp > Core2 Temp > Core3 Temp, with
differences of up to 20 degrees among Core0 and Core3.

-- 
Oscar

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Re: [lm-sensors] Does this makes any sense?

[Jean Delvare]

On Sun, 28 Sep 2008 22:22:50 +0200, Óscar Fuentes wrote:
> This is not a problem with lm-sensors, but an attempt to understand
> what can cause the values it outputs.
> 
> When I start four mprime processes in "torture test" mode on a Q6600
> system it shows a flat 100% CPU usage line and `sensors` report
> temperatures around or below 70 degrees Celsius for each core, which
> is consistent with Intel's specs for a fully loaded CPU:
> 
> oscar@qcore:~/Archivo/prime$ sensors
> coretemp-isa-0000
> Adapter: ISA adapter
> Core 0:      +73.0°C  (crit = +100.0°C)
> 
> coretemp-isa-0001
> Adapter: ISA adapter
> Core 1:      +71.0°C  (crit = +100.0°C)
> 
> coretemp-isa-0002
> Adapter: ISA adapter
> Core 2:      +62.0°C  (crit = +100.0°C)
> 
> coretemp-isa-0003
> Adapter: ISA adapter
> Core 3:      +58.0°C  (crit = +100.0°C)
> 
> However, when compiling an application with "make -j 4" the CPU usage
> is around 95% (which is expected as there is quite a bit of I/O
> involved) but the temperature goes up to 88 degrees on some cores!
> This is a typical output of `sensors` on this scenario:
> 
> coretemp-isa-0000                   
> Adapter: ISA adapter                
> Core 0:      +85.0°C  (crit = +100.0°C)
> 
> coretemp-isa-0001
> Adapter: ISA adapter
> Core 1:      +82.0°C  (crit = +100.0°C)
> 
> coretemp-isa-0002
> Adapter: ISA adapter
> Core 2:      +71.0°C  (crit = +100.0°C)
> 
> coretemp-isa-0003
> Adapter: ISA adapter
> Core 3:      +65.0°C  (crit = +100.0°C)
> 
> What can cause this difference on temperatures, when mprime stresses
> the CPU much more than the compiler?

FWIW: you shouldn't assume that "make -j4" on the kernel will spawn 4
jobs. Having used distcc to build the kernel for some time, I noticed
that make frequently spawns less jobs than I ask for. This only ever
happened to me for kernel builds, but I couldn't explain why it was
happening. Maybe that's why the last 2 cores have a lower temperature.
Try with -j 8 or higher and see if this is still the case.

On why mprime has a lower "mark" than gcc: I can only imagine that the
bottleneck in the mprime case is on something which is "far" from the
thermal sensor, while it is on something which is next the thermal
sensor in the gcc case. CPUs are pretty large and temperature
differences inside the CPU can be significant.

-- 
Jean Delvare

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