CPU C States and Thunderbolt

Hiya,

Apologies if this has been comprehensively addressed elsewhere on the forum. I had a good look with no success (long time lurker).

I have a Simplecom USB hub/ethernet adaptor combo plugged into my 9650 FHD. When this is plugged in, the lowest C power state that my CPU displays will go into (assessed by Throttlestop) is C3.

The TB controller/driver I am using is the most recent available on the Dell driver website. Similarly, the ethernet controller.

I know that the TB15/TB16 docks can cause increased CPU power draw, but is this true of all TB hubs and peripherals?

Or should I just buy a new frickin' hub?

Thanks in advance.

 

I haven't looked at the CPU state but I know that if I plug anything into the USB-C port of Precision 5510 (basically same as XPS15 9550 so it has Thunderbolt) then the cooling fans will come on within 30 seconds due to something heating up. This happens even if there's no traffic through the port. For example the LAN adapter plugged into the port but not connected to LAN cable. I keep hoping that a firmware update will stop this power-wasting (approx 3W extra power drain) but nothing so far.

John

 

Seems similar for me when I use the TB16. Connected I get C3 (and sometimes won't even go beyond C2) on the package (cores use C7). As soon as I disconnect, the package instantly drops to C8.

As for fans, it seems like this is caused by the PCH chip going above a certain temperate threshold. However, the fans can't cool the PCH chip, so it makes no sense turning the fans on for that. I haven't tried connecting the PCH chip to the back panel yet (via thermal pads), to see if that eliminates fans (at least when idling). Still contemplating if I should do that.

 

I've been wondering about C states quite a bit. My 9360 can't seem to access C8 anymore, it used to. I tried disabling thunderbolt entirely to get there but it didn't help.

 

Sounds like it may well be a problem with the TB port in general. Thanks for the replies, all.

 

I don't know if it is a "problem" per se. It is not so efficient today. ThunderBolt is high-performance, resource intensive and is still being refined. As ThunderBolt gets ironed out (and Intel moves it from a separate controller chip to onboard the CPU), it should become more efficient.

I disabled ThunderBolt on my laptop as I find no compelling accessories yet.

I also notice that my 9550s c-states are very sensitve to activity:

- Particularly the package c-states, which are about 80% c8 in idle, but quickly ramp down with simple internet browsing. So I wouldn't worry too much about these unless you are in idle a lot or doing very low intensity work

- Core c-states tend to be more sticky and stick around c7 with some activity. So I focused on getting core c-states at high %

- Begin by getting c0% to say 0.5% on idle per recommendation of @unclewebb , developer of ThrottleStop

 

Fine, a 'feature', then! XD