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On Thu, 9 Feb 2006 20:09:41 +0100 |
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Bernhard Auzinger <e0026053@×××××××××××××××××.at> wrote: |
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> I mean, |
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> how do you get the code of your forked bashes away from your cpu |
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> cache to have it free for kernel code? |
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Forked bash's all use the same image so don't stress the on-chip |
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instruction cache any more than one bash does. You do lose memory for |
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the data needed for each bash, of course - hence the loss of at least |
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one page per process. However unless you actually start swapping to |
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disc (which won't happen if Duncan has no swap set up :) ) this isn't a |
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problem. |
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> A long time ago . . ., I was testing some CFLAGS on my own programs. |
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> I wrote a fast-fourier algorithm myself, only to see the "impressive" |
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> difference between Os, O3 and some other optimisation flags. I fed my |
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> fast-fourier algorithm with a large amount of input. But no matter |
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> how hard I tried to get it faster by changing the flags, it didn't |
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> work. The difference is marginal and not every flag brings |
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> improvement for every program. The only thing that changed a lot was |
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> the time gcc needs to perform those optimisations. |
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I'd guess that your FFT was spending most of its time in unavoidable |
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floating point ops which may explain how various options made little |
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difference. |
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You're right of course - in the end the only way to find out what's |
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actually fastest on a given machine is to try various flags and see |
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what happens. Multiple level caches, long instruction pipelines, |
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paging architecture an a myriad of other things all go to make it |
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difficult to predict exactly what will and won't be faster. |
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P.S. When replying to Duncan's extensive posts, could we trim parts |
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that aren't relevant to the reply? |
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-- |
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Kevin F. Quinn |
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