From: Tom Talpey <tom@talpey.com> To: Mark Zhang <markz@mellanox.com>, Jason Gunthorpe <jgg@ziepe.ca> 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 Rosenbaum <alexr@mellanox.com>, Maor Gottlieb <maorg@mellanox.com>, Leon Romanovsky <leonro@mellanox.com> Subject: Re: [RFC v2] RoCE v2.0 Entropy - IPv6 Flow Label and UDP Source Port Date: Fri, 21 Feb 2020 09:47:12 -0500 Message-ID: <33f075e2-b5c0-53cd-6954-7ac57eeb008f@talpey.com> (raw) In-Reply-To: <c4fc4449-94ed-805e-76d1-6ce856a4fc05@mellanox.com> On 2/19/2020 8:04 PM, Mark Zhang wrote: > On 2/20/2020 1:41 AM, Tom Talpey wrote: >> On 2/19/2020 8:06 AM, Jason Gunthorpe wrote: >>> On Wed, Feb 19, 2020 at 02:06:28AM +0000, Mark Zhang wrote: >>>> The symmetry is important when calculate flow_label with DstQPn/SrcQPn >>>> for non-RDMA CM Service ID (check the first mail), so that the server >>>> and client will have same flow_label and udp_sport. But looks like it is >>>> not important in this case. >>> >>> If the application needs a certain flow label it should not rely on >>> auto-generation, IMHO. >>> >>> I expect most networks will not be reversible anyhow, even with the >>> same flow label? >> >> These are network flow labels, not under application control. If they >> are under application control, that's a security issue. >> > > As Jason said application is able to control it in ipv6. Besides > application is also able to control it for non-RDMA CM Service ID in ipv4. Ok, well I guess that's a separate issue, let's not rathole on it here then. > Hi Jason, same flow label get same UDP source port, with same UDP source > port (along with same sIP/dIP/sPort), are networks reversible? > >> But I agree, if the symmetric behavior is not needed, it should be >> ignored and a better (more uniformly distributed) hash should be chosen. >> >> I definitely like the simplicity and perfect flatness of the newly >> proposed (src * 31) + dst. But that "31" causes overflow into bit 21, >> doesn't it? (31 * 0xffff == 0x1f0000) > > > I think overflow doesn't matter? We have overflow anyway if > multiplicative is used. Hmm, it does seem to matter because dropping bits tilts the distribution curve. Plugging ((src * 31) + dst) & 0xFFFFF into my little test shows some odd behaviors. It starts out flat, then the collisions start to rise around 49000, leveling out at 65000 to a value roughly double the initial one (528 -> 1056). It sits there until 525700, where it falls back to the start value (528). I don't think this is optimal :-) Tom.
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 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 [this message] 2020-02-25 13:20 ` Alex Rosenbaum
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