System extremely slow under light load

Mon Apr 25 12:46:09 UTC 2011

> dev.cpu.X.freq does reflect the current frequency; I don't know whether
> or how any internal clock throttling might be exposed.

 From what I have seen, dev.cpu.X.freq always retains the value I set it 
to. Internal CPU throttling does not seem to be reported this way.

> a bit of hunting found your previous overheating
> problems on a Dell Studio 1557 from April last year:
>
> and your eventual apparent solution which included some fiddling with
> thermal parameters but primarily by disabling p4tcc and acpi_throttle

Yes, that thread described the issues I had with my previous laptop 
before Dell exchanged it. I never posted an actual solution as I never 
found one. The problem only went away because the laptop went away. 
Disabling p4tcc and acpi_throttle may have seemed to address the 
problems at first - but longer-term evaluation showed that the issues 
persisted unchanged.

> hint.p4tcc.0.disabled="1"
> hint.acpi_throttle.0.disabled="1"

I just tried this on my current Dell Studio 1558, with devastating 
results. The first boot attempt ended with the machine shutting down due 
to overheating while loading the kernel. I let it cool down a bit and 
then booted again. This time, I got to my desktop - with a CPU 
temperature of 95°C. If the DSDT was fixed, the machine would have shut 
down at this point.

I only got down the temperature by reducing the maximal temperature to 
1.2GHz again. With the above settings, the machine is idling at 80°C now 
and very sluggish - some internal throttling appears to be active again.

> tz0 looks to be a fan.  It seems unlikely that any temp. sensor inside a
> machine with CPU temp. at 82C could possibly be as low as 26.8C, so this
> value is likely as bogus as the 0.0C CPU reported by tz1.

Yes, the 26.8°C is bogus. It never changes. Unfortunately, I have not 
found a way to fix this reading. The two thermal zones are implemented 
very differently in the DSDT and I have only managed to fix tz1. 
However, there is no second fan inside the laptop. I have taken it apart 
down to the last screw. There is one fan only and that corresponds to tz0.

> This fan should come on at 55C and run fastest above 71C.  If your CPU
> is at 82C and the fan isn't running flat out, it'd overheat for sure.
> tz0.active is -1, not running - but maybe the BIOS is controlling it?

Yes, the BIOS appears to control the fan. The thresholds exposed via 
ACPI seem to be purely informative. Whether I fix the DSDT so that 
temperature readings work or not, the fan turns on at 55°C and speeds up 
at 71°C. It never spins down again after that as the CPU keeps running 
very hot.

> _ACx is N/A here, unless there's a separate CPU fan?  Anyway at bogus
> 0.0C it's never going to trigger passive or active cooling.  You said
> before that with the fixed DSDT to get proper temperature reading here,
> it shut down due to over temperature, which of course it should .. does
> that fixed DSDT include fixing detected tz0 temperature .. if so the fan
> might behave itself without having to use .thermal.user_override=1

See above: Fixing the DSDT makes tz1 work. tz0 remains broken.

> Are you limiting it to 1333 manually, or with powerd's -M switch?

I have tried both. It appears to make no difference whether I use powerd 
-M or just set dev.cpu.0.freq directly.

> Clearly including p4tcc and/or acpi_throttle N*12.5% rates; compare to
> dev.est.0.freq_settings below to figure the freqs added by throttling.
>
> Hopefully this machine will respond as well to disabling both methods as
> your earlier one, as you reported here (same subject, later thread):

See above: Unfortunately, the machine did nor respond well at all. 
Instead, it is overheating even worse.

> Try using C2.  It helps more with some CPUs than others, but it's worth
> a try for further reducing heat, especially at idle.  Ie in rc.conf:
>
> performance_cx_lowest="C2"
> economy_cx_lowest="C2"

I have set dev.cpu.X.cx_lowest="C2" at run-time. If I understand 
correctly, this should achieve the same effect. The CPU does not seem to 
ever make it to C2 though, even after I enable it:

%sysctl dev.cpu | grep cx_usage
dev.cpu.0.cx_usage: 100.00% 0.00% last 270us
dev.cpu.1.cx_usage: 100.00% 0.00% last 399us
dev.cpu.2.cx_usage: 100.00% 0.00% last 403us
dev.cpu.3.cx_usage: 100.00% 0.00% last 404us
dev.cpu.4.cx_usage: 100.00% 0.00% last 323us
dev.cpu.5.cx_usage: 100.00% 0.00% last 313us
dev.cpu.6.cx_usage: 100.00% 0.00% last 174us
dev.cpu.7.cx_usage: 100.00% 0.00% last 137us

>   >  dev.est.0.freq_settings: 1734/45000 1733/45000 1599/41741 1466/38582
>   >  1333/35485 1199/32426 1066/29457 933/26552
>
> With throttling disabled, those are what you should be left with for
> dev.cpu.0.freq_levels.

Yes, these are the frequencies I have available now. 1333 makes the 
machine idle around 85°C, 1999 leads to 78-80°C.

- Bartosz