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Altera_Forum
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8 years ago

Kernel performance with profiling

Hello again guys. Im struggle to understand the results from the profiler of two kernel versions (one with unroll factor of 128 and another with 32) The 32 unroll factor outperforms the 12...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
8 years ago

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I have explained the math behind saturating memory bandwidth here (http://www.alteraforum.com/forum/showthread.php?t=57099&p=232613#post232613). An unroll factor of 32 is likely more than enough to fully saturate the memory bandwidth. Anything more than that will result in a lot of memory contention and lowered performance. You are losing performance due to two reasons: lowered operating frequency, and lowered memory bandwidth due to higher amount of contention. Trying to decipher the numbers reported by the profiler generally results in more confusion, and I have encountered many cases in which the numbers simply do not make sense and contradict each other or the timing results. My recommendation is not to rely too much on those numbers.

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Thanks mate! HRZ you're my salvation ;)

My doubt was because of the stall parameter, it would make sense that were more high because of the memory contention...