Memory transaction instructions

[Matthew Wilcox]

On Mon, Jan 16, 2023 at 02:08:15PM +0000, David Howells wrote:
> Hi Linus,
> 
> I'm not sure how relevant it is to the topic, but I seem to remember you
> having a go at implementing spinlocks with x86_64 memory transaction
> instructions a while back.  Do you have any thoughts on whether these
> instructions are ever likely to become something we can use?

Ever is a long time, but not while they're still buggy:

https://en.wikipedia.org/wiki/Transactional_Synchronization_Extensions

and not while they're not actually available on a vast majority of
x86 hardware.  ie AMD needs to implement them, make them available as
standard, forcing Intel to enable them globally instead of restricting
them to those who pay the $2.50/month subscription fee.