Re: [patch] prefer TSC over PM Timer

[Alan Cox]

On Maw, 2004-11-16 at 00:23, dean gaudet wrote:
> i've heard other folks have independently run into this problem -- in fact 
> i see the most recent fc2 kernels already do this.  i'd like this to be 
> accepted into the main kernel though.

IMHO it was a mistake to make this change in FC2.

> the x86 PM Timer is an order of magnitude slower than the TSC for 
> gettimeofday calls.  i'm seeing 8%+ of the time spent doing gettimeofday 
> in someworkloads... and apparently kernel.org was seeing 80% of its time 
> go to gettimeofday during the fc3-release overload.  PM timer is also less 
> accurate than TSC.

Nobody guarantees that the TSC is clocked at the same rate per CPU and
several power management schemes break it. I see it break on my Thinkpad
600 and its one reason I have to replace the FC kernel with a 2.6-ac
kernel on that system.

Is gettimeofday supposed to return the right value or be fast ?

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