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On Wednesday 14 February 2007, brullo nulla wrote: |
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> > Most likely you only looked at user cpu % and neglected to list the |
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> > system and niced times as well. |
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> > |
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> > p.s. golden rule: ps lies. top lies. free lies. |
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> > Don't believe the readings they give, rather interpret them in |
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> > context. |
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> |
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> sob. it's not the first time I hear this. What should I believe to |
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> really know my system state? |
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You should use ps, top and free of course! Just realize that they lie... |
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Actually they don't lie, they give an average. You also need to |
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understand what is going on. Without getting into the details of |
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exactly what a cpu is doing, it's performing actions millions of times |
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a second. In the time it takes top to update (2 seconds), the kernel |
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could have started and shut down several thousand forked processes. So |
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trying to measure something that changes so fast is a waste of time. |
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Also, there's the kernels internal timer. It's set by default to 100Hz, |
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which means that the kernel updates it's own counters 100 times a |
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second. It's quite possible to use and discard lots of memory in that |
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gap and for it to never even show up in the kernel's counters. Raising |
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the timer frequency for 1000Hz for a desktop gives more accurate |
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results, but they are still just an average. |
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Same with memory - the kernel allocates it out and shares the same |
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memory between several processes as it sees fit. And does what it wants |
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to with swap as well. Again, trying to find out the current state of |
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the system is useless as by the time you read it, it has changed 16 |
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million times.... |
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When we say that top lies, we really mean that it is giving you an |
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average over a looooooong period of cpu time, and you should interpret |
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it as such. It's a trend, not an instant value. |
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alan |
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-- |
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Optimists say the glass is half full, |
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Pessimists say the glass is half empty, |
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Developers say wtf is the glass twice as big as it needs to be? |
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|
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Alan McKinnon |
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alan at linuxholdings dot co dot za |
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+27 82, double three seven, one nine three five |
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-- |
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gentoo-user@g.o mailing list |
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