PPPoE - Single Core - SMT / Hyper Threading On or Off

RobbieTT

With the extant PPPoE issue limiting the traffic through a single core, should SMT be switched-off to preserve the maximum throughput path for PPPoE?

For example, in a 4 core / 8 thread system would the maximum PPPoE WAN throughput be maintained with SMT off, or will it be unhindered by the 'sharing' of the core with SMT selected on?

(I cannot test this myself as I have 4-core with no Hyper Threading capability).

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stephenw10

I would expect to get better single thread performance with hyper-threading disabled, yes. Though it's probably a pretty small difference.

RobbieTT

@stephenw10
Thanks Steve. It's not something I had thought about until asked. FreeBSD seems to liberally bounce the actual core being used for PPPoE from core to core on my 6100 but I guess it makes sense that the PPPoE would prefer its own pipe, rather than sharing through SMT, when running its queues and FQ_CoDel.

I've got a new 8-core/16-thread Xeon-D mini-server on order and I will probably run pfSense on it for testing and/or acting as a spare device. It probably runs fast enough for high-bandwidth PPPoE whatever the SMT setting but I will try it either way, just to have a look.

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tman222

@RobbieTT said in PPPoE - Single Core - SMT / Hyper Threading On or Off:

@stephenw10
Thanks Steve. It's not something I had thought about until asked. FreeBSD seems to liberally bounce the actual core being used for PPPoE from core to core on my 6100 but I guess it makes sense that the PPPoE would prefer its own pipe, rather than sharing through SMT, when running its queues and FQ_CoDel.

I've got a new 8-core/16-thread Xeon-D mini-server on order and I will probably run pfSense on it for testing and/or acting as a spare device. It probably runs fast enough for high-bandwidth PPPoE whatever the SMT setting but I will try it either way, just to have a look.

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@RobbieTT - which Xeon D CPU / server did you end up going with? I'm a fan of that platform - had a Xeon D-1518 based system that I used with pfSense for a number years with zero issues, and recently upgraded to a newer Xeon D-1718T system which I'm also very happy with. Performance is great on the somewhat limited testing I have done so far - the 1718T based system will route at 10Gbit/s between two 10Gbit LAN segments with a single iperf3 stream while the 1518 based system was limited to 6-7 Gbit/s.

Regarding Hyper-Threading, I have left it on ever since I came across the machdep.hyperthreading_intr_allowed tunable which enables interrupts on hyperthreaded cores:

https://svnweb.freebsd.org/base?view=revision&revision=354338

RobbieTT

@tman222 said in PPPoE - Single Core - SMT / Hyper Threading On or Off:

Xeon D-1718T

I went with the D-1736NT (8-core QAT) wrapped in the very familiar Supermicro short-depth design (SYS-510D-8C-FN6P).

I did look at the 4-core QAT version for the lower TDP but they were exceptionally hard / impossible to find in the UK and not much cheaper than the 8C. No doubt I will end up running a few things on it so the extra cores will probably get to stretch their legs at some point.

The rest of it will come from stuff existing I have kicking around - a couple of 16GB RDIMMs, Optane (M.2 and/or U.2), slimSAS to 4x or 8x SATA SSDs are all candidates. These things always tend to get 'played' with. Tempted to try Proxmox too.