There's a lot of code which accesses the current interpreter state especially under free-threading via PyInterpreterState_Get. Currently to lookup interpreter state first the thread state is accessed then read by ts->interp but it can be optimized to be stored in a thread local variable _Py_tss_current_interp so that it can be read directly.

Linked PRs

• gh-140544: cleanup HAVE_THREAD_LOCAL checks in pystate.c #140547
• gh-140544: store pointer to interpreter state as a thread local for fast access #140573
• gh-140544: use faster _PyInterpreterState_GET for type lock #140584
• gh-140544: fix build for including pycore_pystate.h when HAVE_THREAD_LOCAL is not defined #140623
• gh-140544: Always assume that thread locals are available #140690