On Fri, 31 Jul 2026 16:53:45 +0200 Morten Brørup <[email protected]> wrote:
> +TO: x86 maintainers, ThunderX maintainers > > > From: Stephen Hemminger [mailto:[email protected]] > > Sent: Wednesday, 29 July 2026 19.54 > > > > The generic and C11 lock-free stack implementations differ only in > > memory ordering. The generic version uses a full barrier where its > > own comments state an acquire fence is sufficient, and seq_cst for > > all length counter operations. > > > > Only x86 and ThunderX still used the generic version. On x86 the > > switch removes a locked add per CAS attempt in push and pop; TSO > > provides the acquire semantics. On ThunderX the pop fence weakens > > from dmb ish to dmb ishld and the push fence goes away. Unlike the > > ring, no platform selected the generic stack for measured > > performance reasons. > > > > Remove it and use the C11 implementation everywhere. > > The lack of measured performance difference documentation is not a valid > reason to remove the generic version! > > It would be reasonable to assume that x86 (and ThunderX) use the generic > version for non-insignificant performance reasons. > > If there is no performance difference, I agree with this patch. Otherwise not. > This could be verified by providing the missing measurements. > The reason is that smp_mb's need to go away. The other option is revise to replace with thread fence, at which point it becomes the same as generic code.
