• Mike (25/25) Dec 13 2007 Hi!
• Tomas Lindquist Olsen (3/33) Dec 14 2007 RDTSC is no longer safe on multicore systems. Wikipedia has some notes o...
• BCS (3/21) Dec 14 2007 this is only valid if the thread is not context switched.

Mike <vertex gmx.at> writes:

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 periodicall=
y,  =

takes time of start in[t] at the entry point and time of exit out [t] wi=
th  =

"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 =3D 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

-- =

Using Opera's revolutionary e-mail client: http://www.opera.com/mail/

Tomas Lindquist Olsen <tomas famolsen.dk> writes:

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

BCS <ao pathlink.com> writes:

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.