On Thu, 26 Oct 2023 14:59:13 -0400 Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote: > > for a rough implementation of a 'xchg()' without SMP coherency, just > > cpu-local one (ie atomic wrt being preempted by the kernel, but not > > atomic wrt other CPU's accessing the same variable concurrently) > > Actually Steven does not need a xchg to test-and-set a single bit which > is only accessed concurrently between kernel and userspace from the same > thread. Either "bts" or "andb" should work fine. Hmm, how would bts work? Doesn't that just set a bit? I need to clear one bit while seeing if another bit is set. I could also use subl, as that would also atomically clear the bit. -- Steve
