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

* Peter Zijlstra:

On Mon, Jan 31, 2022 at 10:19:09PM +0100, Florian Weimer wrote:

quoted

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?