On Fri, May 31, 2019 at 08:58:19PM +0200, Roman Penyaev wrote: > On 2019-05-31 18:51, Peter Zijlstra wrote: > > But like you show, it can be done. It also makes the thing wait-free, as > > opposed to merely lockless. > > You think it's better? I did not like this variant from the very > beginning because of the unnecessary complexity. But maybe you're > right. No busy loops on user side makes it wait-free. And also > I can avoid c11 in kernel using cmpxchg along with atomic_t. Imagine the (v)CPU going for an extended nap right between publishing the new tail and writing the !0 entry. Then your userspace is stuck burning cycles without getting anything useful done.
