Re: changing the sample rate

[William C. <wc...@re...>]

Shlomi Ben-Shabat wrote:
> hi
> while using oprofile
> I wanted to reduce the time between the samples, so I tried: 
>  
> # opcontrol --event=CPU_CLK_UNHALTED:30000:0:1
>  
> but I got in return:
>  
> "You cannot specify any performance counter events
> because OProfile is in timer mode."
>  
> what does it mean?
> and how can I control the sample rate?
>  
> thanks
> Shlomi

That means that OProfile didn't know what kind of performance monitoring 
hardware your processor has or it couldn't initialize it. OProfile has a fall 
back mechanism that is set to take a sample each jiffy. So if there are 100 
jiffies per second you will get 100 samples per second you cannot change the 
timer smaple rate. The local apic support needs to work to be able to route 
interrupts from the performance counter overflow to the processor.

What kind of machine are you using OProfile on? What is the output of 
/proc/cpuinfo? Also take a look through the /var/log/messages to see if there is 
some messages about local apic being disabled.

-Will