Hi!

It's not really D related, I know, but I don't know where else to ask.

So: I've got this little class that measures in/out time of threads with the rdtsc assembler opcode. The relevant thread gets started periodically, takes time of start in[t] at the entry point and time of exit out [t] with "scope (exit) ...".

This gives me the following measurments:

in[t]   // thread entered (current iteration)
out[t]  // thread exited (current iteration)
in[t-1] // thread entered (last iteration)

And the following formula:

cpuload = 100 * (out[t] - in[t]) / (in[t] - in[t-1]);

to get the cpu load in %.

Now I've tested this and I'm not quite sure. The results are at least somewhat  reasonable, although they seem to be double the real value (I've got a dual core system) so that might explain that.

But before guessing around I thought I'll ask here if this way of measuring is completely wrong or if there's a better way to do that.

-Mike

-- 
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Mike wrote:
> Hi!
> 
> It's not really D related, I know, but I don't know where else to ask.
> 
> So: I've got this little class that measures in/out time of threads with the rdtsc assembler opcode. The relevant thread gets started periodically, takes time of start in[t] at the entry point and time of exit out [t] with "scope (exit) ...".
> 
> This gives me the following measurments:
> 
> in[t]   // thread entered (current iteration)
> out[t]  // thread exited (current iteration)
> in[t-1] // thread entered (last iteration)
> 
> And the following formula:
> 
> cpuload = 100 * (out[t] - in[t]) / (in[t] - in[t-1]);
> 
> to get the cpu load in %.
> 
> Now I've tested this and I'm not quite sure. The results are at least somewhat  reasonable, although they seem to be double the real value (I've got a dual core system) so that might explain that.
> 
> But before guessing around I thought I'll ask here if this way of measuring is completely wrong or if there's a better way to do that.
> 
> -Mike
> 

RDTSC is no longer safe on multicore systems. Wikipedia has some notes on it:
http://en.wikipedia.org/wiki/RDTSC

Reply to mike,

> Hi!
> 
> It's not really D related, I know, but I don't know where else to ask.
> 
> So: I've got this little class that measures in/out time of threads
> with  the rdtsc assembler opcode. The relevant thread gets started
> periodically,  takes time of start in[t] at the entry point and time
> of exit out [t] with  "scope (exit) ...".
> 
> This gives me the following measurments:
> 
> in[t]   // thread entered (current iteration)
> out[t]  // thread exited (current iteration)
> in[t-1] // thread entered (last iteration)
> And the following formula:
> 
> cpuload = 100 * (out[t] - in[t]) / (in[t] - in[t-1]);
> 

this is only valid if the thread is not context switched. 

the ony reliable way to get CPU loads I can think of would be to ask the OS.