[Cake] [LEDE-DEV] Cake SQM killing my DIR-860L - was: [17.01] Kernel: bump to 4.4.51
john at yates-sheets.org
Thu Mar 2 18:55:29 EST 2017
On Thu, Mar 2, 2017 at 4:10 PM, Dave Täht <dave at taht.net> wrote:
> As for speeding up hashing, I've been looking over various algorithms to
> do that for years now, I'm open to suggestions. The fastest new ones
> tend to depend on co-processor support. The fastest I've seen relies on
> the CRC32 instruction which is only in some intel platforms.
This is an area where I have a fair amount of experience.
It is a misconception that CRC is a good hash function. It is good
at detecting errors but has poor avalanche performance.
What are the requirements for this hashing function?
- How much data is being hashed? (I would guess a limited number
of bytes rather than an entire packet payload.)
- What is the typical number of hash table buckets? Must it be a
power of 2? Or are you willing to make it a prime number?
Assuming you can afford a 1KB lookup table I would suggest
the SBox hash in figure four of this article:
The virtue of a prime number of buckets is that when you mod
your 32-bit hash value to get a bucket index you harvest _all_
of the entropy in the hash, not just the entropy in the bits you
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