linux-kernel - Re: [PATCH sched_ext/for-6.13] sched_ext: Do not enable LLC/NUMA optimizations when domains overlap

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Message-ID: <Zyq5cX9fLE-3wZSx@slm.duckdns.org>
Date: Tue, 5 Nov 2024 14:33:53 -1000
From: Tejun Heo <tj@...nel.org>
To: Andrea Righi <arighi@...dia.com>
Cc: David Vernet <void@...ifault.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH sched_ext/for-6.13] sched_ext: Do not enable LLC/NUMA
 optimizations when domains overlap

Hello,

On Wed, Nov 06, 2024 at 01:29:08AM +0100, Andrea Righi wrote:
...
> Let's say we have 2 NUMA nodes, each with 2 sockets, and each socket
> has its own L3 cache. In this case, numa_cpus will be larger than
> llc_cpus, and enabling both NUMA and LLC optimizations would be
> beneficial.
> 
> On the other hand, if each NUMA node contains only 1 socket, numa_cpus
> and llc_cpus will overlap completely, making it unnecessary to enable
> both NUMA and LLC optimizations, so we can have just the LLC in this
> case.
> 
> Would something like this help clarifying the first test?

I was more thinking about the theoretical case where one socket has one LLC
while a different socket has multiple LLCs. I don't think there are any
systems which are actually like that but there's nothing in the code which
prevents that (unlike a single CPU belonging to multiple domains), so it'd
probably be worthwhile to explain why the abbreviated test is enough.

Thanks.

-- 
tejun