### Re: Re: Benchmarking Tests

by kidd (Curate)
 on Apr 30, 2003 at 23:18 UTC ( #254528=note: print w/replies, xml ) Need Help??

in reply to Re: Benchmarking Tests

The thing is that recently my client's sever has been overloaded and they blamed one of my script, that's the reason I checked all of them.

We are allowed to use 3% of the total CPU usage, so that is like from 3 to 5 CPU's but the server load we are using is between 10 to 15.

What I wanted to do is check if one of my script where doing the server load of one of the other host, because we are on a shared plan.

I though that my CPU usage per script was very normal, and we may have up to 20 users at the same time. So I made a little math and thought:

"If my script is using 0.15 CPU and lets say that 20 users use it at the sames time(it's very unusual), then it would be 3 CPU, that is not close to 10 or to 15".

I just wanted to be sure that my script aren't using a lot of server load...

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Re: Re: Re: Benchmarking Tests
by tedrek (Pilgrim) on May 01, 2003 at 07:15 UTC
You appear to be mixing up CPU usage and Load. in particular your example of 0.15 CPU * 20 Users = 3 Load doesn't make sense as 0.15 is a percentage and load is absolute

Load is the number of processes that are waiting for time on the CPU. That would be the 10 or 15

% CPU is the amount of real time that the process spent actually running eg 0.15.

So in your example if your script was taking 0.15 CPU over 1 second and you had 20 users running it simultaneously you would be trying to use 20 * 0.15 = 3.00 CPU which means that you will be using 100% of the CPU for 3 seconds. and that would translate into roughly 20 load at 0 seconds 14 load at 1 second 7 load at 2 seconds and 0 load at 3 seconds. Assuming each request ran to completion 1 after the other. Which they probably won't what with the vagaries of I/O and scheduling.

And of course if you have a multi proc box then the real time taken is % CPU / # of CPU's

I'm not sure if the %CPU time is the percentage the process uses over a fixed length of time eg 1 second. or if it's the percentage used over the length of time it took to run to completion.

Anyway I hope that explains the difference between Load and CPU usage ( and I hope it's reasonably accurate). I also hope it helps you find the problem, and of course as other ppl have already said, Do a actual test, *this* is just to help you interpret the numbers a bit better :). Also Load is usually averaged over the last minute 5 minutes and 15 minutes

Re: Re: Re: Benchmarking Tests
by Anonymous Monk on Apr 30, 2003 at 23:47 UTC

Post the code. Your much more likely to get good answers if you do.

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