Re: [PATCH] transition latency of speedstep-ich (third try)

[Eric Piel <Eric.Piel@tremplin-utc.net>]

28.11.2005 23:19, Pallipadi, Venkatesh wrote/a écrit:
>>-----Original Message-----
>>From: Mattia Dongili [mailto:malattia@linux.it] 
>>
>>I just build speedstep-ich with transition_latency = 250
>>I'll let you know how it goes. Are you interested?
Actually, the ondemand governor is quite safe on this side and multiply 
this value by 1000, so it shouldn't bring any problem anyway :-)

>>Maybe it's already been discussed, but how bad would be trying to
>>measure transition latency at runtime?
>>
> 
> 
> 
> Yes. I was thinking the same thing. As this latency may be different on P3-M and P4-M, may be we can do with a measurement at boot time and use it, rather than hardcoding these values. However, I think we will have to do that by using gettimeofday or some such higherlevel call instead of using pmtimer as pmtimer may not be available on all systems at all times. Otherwise, we may end up all sort of pmtimer/pit/hpet timer code in this driver.
> 
Sounds interesting :-) Especially as speedstep-ich already does at least 
2 frequency transitions while initialising, it should be fairly easy to 
implement. I'm more concerned about the time measurement. What could be 
done is to use gettimeofday() and check that the result is reasonable 
(not too big nor too small), if it's not we just put something 
conservative, like 500us.

Eric