Re: [RFC PATCH 1/2] rseq: extend struct rseq with numa node id

[Florian Weimer]

* Peter Zijlstra:

> On Mon, Jan 31, 2022 at 10:19:09PM +0100, Florian Weimer wrote:
>> It can be used to implement getcpu purely in userspace, too.  I had
>> plan to hack this together with a node ID cache in TLS, which should
>> offer pretty much the same functionality (except for weird CPU
>> topology changes which alter the node ID of a previously used CPU).
>
> PowerPC does that quite a lot..

How so?  Why make it especially hard for userspace?