linux-kernel - Re: [PATCH v2 08/10] um: Add initial SMP support

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Message-ID: <03cb4661a6135a641c5a3779f2cb424356b8e345.camel@sipsolutions.net>
Date: Thu, 11 Sep 2025 11:32:56 +0200
From: Johannes Berg <johannes@...solutions.net>
To: Tiwei Bie <tiwei.bie@...ux.dev>, richard@....at, 
	anton.ivanov@...bridgegreys.com
Cc: linux-um@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	benjamin@...solutions.net, arnd@...db.de, tiwei.btw@...group.com
Subject: Re: [PATCH v2 08/10] um: Add initial SMP support

On Sun, 2025-08-10 at 13:51 +0800, Tiwei Bie wrote:
> From: Tiwei Bie <tiwei.btw@...group.com>
> 
> Add initial symmetric multi-processing (SMP) support to UML. With
> this support enabled, users can tell UML to start multiple virtual
> processors, each represented as a separate host thread.
> 
> In UML, kthreads and normal threads (when running in kernel mode)
> can be scheduled and executed simultaneously on different virtual
> processors. However, the userspace code of normal threads still
> runs within their respective single-threaded stubs.
> 
> That is, SMP support is currently available both within the kernel
> and across different processes, but still remains limited within
> threads of the same process in userspace.

Another thing that isn't covered is anything relating to interrupt
affinity, I guess? Is that automatically not working, or will it look
like you can change things but that not do anything?

I don't think it's important now (though eventually I would actually
like to have it for our simulations), but was just thinking about it.

johannes