Pawan Singh wrote:
>
> 1. The piece of code I am running is a user process.
> 2. Only reason I tried CLI() and STI() is so that I can find out how much
> time does the CPU take to execute the code - just as a benchmark. I will
> never use cli and sti in the user land.
>
> 3. I finally have one more clue. It does not matter if it is a floating
> point operation inside the loop. One gets the same results with integer
> operations. The result gets worse and worse depending on the number of
> instructions in the loop.
>
> 4. I have made sure that compiler has not optimized anything. The piece of
> code I typed was just a quick demonstration. Add to the code something after
> the loop (like printf) which uses the sum total being produced by the loop.
>
> So in short it seems to me is this - for one integer add:
> 1. Interrupts turned off: 1000000 integer additions take 10ms.
> 2. With interrupts turned on 10000000 integer additions take 270ms.
>
> To me it is 27 times kernel overhead.
>
> If I increase the number of integer instructions in the loop to what
> floating point code does for two float additions i.e. 100 instructions,
> 1. Interrupts turned off: 10000 loop interations take 10ms.
> 2. With interrupts turned on 100000 loop iterations take 1000 to 2000
> seconds.
>
:):) And how do you think the timer get updated if you turn interrupts off :):) the
:10ms got me thinking this is probably your problem.
To do you measure you have to use the waltime clock increase the loop size so it takes
10 sek and see if you have any difference or get your time directly from the RTC if
you have any.
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