[userbinator]

Relatively cool: between 60 and 70 degrees Celsius.

That sounds a bit on the high end, considering that 65 is the highest my system (early i7) goes when fully loaded... but then looking at the temperature graph, it looks like they're really pushing them to the limits and letting thermal throttling take care of the rest - the spec for that particular model is ~80 max.

Since this is a VM, there's always a remote chance that they can trap the MSR reads and return whatever data they want. (Maybe it could even be used as a convert channel...?)

[idlewords]

In a data center, it probably makes sense to cool this stuff only as much as necessary. I bet the 60-70 degree figure is the result of some extensive analysis and experimentation by Amazon.

[brendangregg]

The thermal throttle limit (PROCHOT), according to the MSRs, is 95. I did read through the various thermal status and thermal log MSRs, which were always zero, suggesting we aren't thermal throttling. Although I'm not sure those MSR bits are exposed by Xen. (They probably are, since the other bits in the same MSR are.)

Just checking the Intel manual docs:

"• Thermal Status (bit 0, RO) — This bit indicates whether the digital thermal sensor high-temperature output signal (PROCHOT#) is currently active. Bit 0 = 1 indicates the feature is active. This bit may not be written by software; it reflects the state of the digital thermal sensor.

• Thermal Status Log (bit 1, R/WC0) — This is a sticky bit that indicates the history of the thermal sensor high temperature output signal (PROCHOT#). Bit 1 = 1 if PROCHOT# has been asserted since a previous RESET or the last time software cleared the bit. Software may clear this bit by writing a zero."

I was checking both, and both were zero.

So if we aren't thermal throttling, then I guess it still may be the fans...

[tachyonbeam]

> That sounds a bit on the high end, considering that 65 is the highest my system (early i7) goes when fully loaded

But their i7 is probably stuffed in a room with 10000 other machines.