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Observer te7a
Observer
620 Views
Registered: ‎05-26-2017

bigger kernel versus multiple instances of a small kernel

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if I have a kernel, say with some loop unrolled either fully or with a factor of say 32,

 

Which option is better (for build process to finish faster, pass timing....etc)

- double the unroll factor to 64

- have 2 instances of the kernel with unroll factor of 32 

 

The reason I'm asking is because I have been trying to double the unroll factor, my resource usage is about 14% before doubling, when doubling to 64, the build fails with errors in the last phase (@ bitstream generation) 

I have tried so many trials, but so far whenever my resource utilization is over 25% of LUTs the build fails!

 

So I was wondering if 2 instances of the kernel will be easier for the tool to build or it will give me the same result?

 

here is the last error I got when I tried to unroll 64, it failed because of frequency scalling

 

ERROR: [VPL-4] auto frequency scaling failed because the auto scaled frequency '49.6 MHz' is lower than the minimum frequency limit supported by the runtime (60 MHz).
ERROR: [VPL 60-704] Integration error, problem implementing dynamic region, route_design ERROR
ERROR: [VPL 60-806] Failed to finish platform linker
ERROR: [XOCC 60-398] vpl failed
ERROR: [XOCC 60-626] Kernel link failed to complete
ERROR: [XOCC 60-703] Failed to finish linking
 
 
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Xilinx Employee
Xilinx Employee
526 Views
Registered: ‎01-12-2017

Re: bigger kernel versus multiple instances of a small kernel

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Moderator
Moderator
577 Views
Registered: ‎11-04-2010

Re: bigger kernel versus multiple instances of a small kernel

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Please try to evaluate both of the kernel code in HLS to see how fast the kernel can achieve first.

If the frequency is too slow, then you can try to optimize the kernel with HLS pragma.

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Observer te7a
Observer
538 Views
Registered: ‎05-26-2017

Re: bigger kernel versus multiple instances of a small kernel

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I was asking this question hoping for a technical difference between doubling kernel size versus creating 2 instances of a kernel.

 

after trying it out, seems like the tool was able to create 2 instances but can't double the resources used and keep it as 1 kernel.

 

so it seems like there is a difference between the two options 

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Xilinx Employee
Xilinx Employee
527 Views
Registered: ‎01-12-2017

Re: bigger kernel versus multiple instances of a small kernel

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