From: Jason Gunthorpe <jgg@ziepe.ca>
To: Tom Talpey <tom@talpey.com>
Cc: Alex Rosenbaum <rosenbaumalex@gmail.com>,
RDMA mailing list <linux-rdma@vger.kernel.org>,
Eran Ben Elisha <eranbe@mellanox.com>,
Yishai Hadas <yishaih@mellanox.com>,
"Alex @ Mellanox" <alexr@mellanox.com>,
Maor Gottlieb <maorg@mellanox.com>,
Leon Romanovsky <leonro@mellanox.com>,
Mark Zhang <markz@mellanox.com>
Subject: Re: [RFC v2] RoCE v2.0 Entropy - IPv6 Flow Label and UDP Source Port
Date: Thu, 13 Feb 2020 11:41:10 -0400
Message-ID: <20200213154110.GJ31668@ziepe.ca> (raw)
In-Reply-To: <62f4df50-b50d-29e2-a0f4-eccaf81bd8d9@talpey.com>
On Thu, Feb 13, 2020 at 10:26:09AM -0500, Tom Talpey wrote:
> > If both src & dst ports are in the high value range you loss those
> > hash bits in the masking.
> > If src & dst port are both 0xE000, your masked hash equals 0. You'll
> > get the same hash if both ports are equal 0xF000.
>
> Sure, but this is because it's a 20-bit hash of a 32-bit object. There
> will always be collisions, this is just one example. My concern is the
> statistical spread of the results. I argue it's not changed by the
> proposed bit-folding, possibly even damaged.
I've always thought that 'folding' by modulo results in an abnormal
statistical distribution
The point here is not collisions but to have a hash distribution which
is generally uniform for the input space.
Alex, it would be good to make a quick program to measure the
uniformity of the distribution..
Jason
next prev parent reply index
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-08 14:26 Alex Rosenbaum
2020-01-15 9:48 ` Mark Zhang
2020-02-06 14:18 ` Tom Talpey
2020-02-06 14:35 ` Jason Gunthorpe
2020-02-06 14:39 ` Alex Rosenbaum
2020-02-06 15:19 ` Tom Talpey
2020-02-08 9:58 ` Alex Rosenbaum
2020-02-12 15:47 ` Tom Talpey
2020-02-13 11:03 ` Alex Rosenbaum
2020-02-13 15:26 ` Tom Talpey
2020-02-13 15:41 ` Jason Gunthorpe [this message]
2020-02-14 14:23 ` Mark Zhang
2020-02-15 6:27 ` Mark Zhang
2020-02-18 14:16 ` Tom Talpey
2020-02-18 17:41 ` Tom Talpey
2020-02-19 1:51 ` Mark Zhang
2020-02-19 2:01 ` Tom Talpey
2020-02-19 2:06 ` Mark Zhang
2020-02-19 13:06 ` Jason Gunthorpe
2020-02-19 17:41 ` Tom Talpey
2020-02-19 17:55 ` Jason Gunthorpe
2020-02-20 1:04 ` Mark Zhang
2020-02-21 14:47 ` Tom Talpey
2020-02-25 13:20 ` Alex Rosenbaum
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