On 12/8/18 7:43 PM, Warner Losh wrote: > > > On Sat, Dec 8, 2018, 8:36 PM Kevin Bowling <kevin.bowl...@kev009.com > <mailto:kevin.bowl...@kev009.com> wrote: > > On Sat, Dec 8, 2018 at 12:09 AM Mateusz Guzik <mjgu...@gmail.com > <mailto:mjgu...@gmail.com>> wrote: > > > > > Fully satisfying solution would be that all architectures get 64-bit > > ops, even if in the worst case they end up taking a lock. Then > > subsystems would not have to ifdef on anything. However, there > > was some opposition to this proposal and I don't think this is > > important enough to push. > > Mateusz, > > Who is opposing this particular polyfill solution? Scott Long brought > up a situation in driver development where this would be useful as > well. The polyfills lower the cognitive load and #ifdef soup which > are the right call here regardless of performance on toy ports. > > > I don't recall seeing the opposition either. It would have to be a global > lock for all 64bit atomics.... but I think it would only be 2 atomics on > those architectures.
It would have to be a spin lock, so in the case of unrl you would be trading an operation on one of N regular mutexes for a single spin lock that was also contested by other things. This would be pretty crappy. For drivers that aren't actually used on platforms without 32-bit atomics we can simply not build them in sys/modules/Makefile or not put them in GENERIC. For something in the core kernel like unrl I think we will have to do what Mateusz has done here. -- John Baldwin _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
