Comment 1:

I believe that changing from g to m is a mistake.
The most frequently accessed thread-local data is g->stackguard0, which is in g. It is
accessed once per function call. g is also much easier to reason about in programs,
because it cannot change from line to line as a particular function executes.
Eventually I would like to put g back into a dedicated register on amd64, like we do on
arm. Then getting at g->stackguard0 will be just one load, and getting at m will be just
one load too.

Comment 2:

> The most frequently accessed thread-local data is g->stackguard0, which is in g.
Yes, it's the most frequently accessed, that's I propose to move it to M. But there are
also m->mcache, m->locks, m->p and m->ptr/scalarargs. Duplicating them in G looks bad
because it will bloat G and open door to bugs. While what was called stackguard0 can
moved to M rather than duplicated.
> g is also much easier to reason about in programs, because it cannot change from line
to line as a particular function executes.
It's true that it can change, but I don't see how naming things differently changes
something. It can change regardless of whether you call it 'm' or 'g->m'. If you want to
prevent m from changing, you do 'm->locks++' or 'g->m->locks++'. No difference (other
than additional indirection).