> -----Original Message-----
> From: Michael Kelley <[email protected]>
> Sent: Tuesday, January 9, 2024 2:23 PM
> To: Souradeep Chakrabarti <[email protected]>; KY Srinivasan
> <[email protected]>; Haiyang Zhang <[email protected]>;
> [email protected]; Dexuan Cui <[email protected]>;
> [email protected]; [email protected]; [email protected];
> [email protected]; Long Li <[email protected]>; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; linux-
> [email protected]
> Cc: Souradeep Chakrabarti <[email protected]>; Paul Rosswurm
> <[email protected]>
> Subject: RE: [PATCH 3/4 net-next] net: mana: add a function to spread IRQs per
> CPUs
>
> [Some people who received this message don't often get email from
> [email protected]. Learn why this is important at
> https://aka.ms/LearnAboutSenderIdentification ]
>
> From: Souradeep Chakrabarti <[email protected]> Sent:
> Tuesday, January 9, 2024 2:51 AM
> >
> > From: Yury Norov <[email protected]>
> >
> > Souradeep investigated that the driver performs faster if IRQs are
> > spread on CPUs with the following heuristics:
> >
> > 1. No more than one IRQ per CPU, if possible;
> > 2. NUMA locality is the second priority;
> > 3. Sibling dislocality is the last priority.
> >
> > Let's consider this topology:
> >
> > Node 0 1
> > Core 0 1 2 3
> > CPU 0 1 2 3 4 5 6 7
> >
> > The most performant IRQ distribution based on the above topology
> > and heuristics may look like this:
> >
> > IRQ Nodes Cores CPUs
> > 0 1 0 0-1
> > 1 1 1 2-3
> > 2 1 0 0-1
> > 3 1 1 2-3
> > 4 2 2 4-5
> > 5 2 3 6-7
> > 6 2 2 4-5
> > 7 2 3 6-7
>
> I didn't pay attention to the detailed discussion of this issue
> over the past 2 to 3 weeks during the holidays in the U.S., but
> the above doesn't align with the original problem as I understood
> it. I thought the original problem was to avoid putting IRQs on
> both hyper-threads in the same core, and that the perf
> improvements are based on that configuration. At least that's
> what the commit message for Patch 4/4 in this series says.
>
> The above chart results in 8 IRQs being assigned to the 8 CPUs,
> probably with 1 IRQ per CPU. At least on x86, if the affinity
> mask for an IRQ contains multiple CPUs, matrix_find_best_cpu()
> should balance the IRQ assignments between the CPUs in the mask.
> So the original problem is still present because both hyper-threads
> in a core are likely to have an IRQ assigned.
>
> Of course, this example has 8 IRQs and 8 CPUs, so assigning an
> IRQ to every hyper-thread may be the only choice. If that's the
> case, maybe this just isn't a good example to illustrate the
> original problem and solution. But even with a better example
> where the # of IRQs is <= half the # of CPUs in a NUMA node,
> I don't think the code below accomplishes the original intent.
>
> Maybe I've missed something along the way in getting to this
> version of the patch. Please feel free to set me straight. :-)
>
> Michael
I have the same question as Michael. Also, I'm asking Souradeep
in another channel: So, the algorithm still uses up all current
NUMA node before moving on to the next NUMA node, right?
Except each IRQ is affinitized to 2 CPUs.
For example, a system with 2 IRQs:
IRQ Nodes Cores CPUs
0 1 0 0-1
1 1 1 2-3
Is this performing better than the algorithm in earlier patches? like below:
IRQ Nodes Cores CPUs
0 1 0 0
1 1 1 2
Thanks,
- Haiyang
