On Mon, Feb 15, 2016 at 10:50:29AM +0000, Will Deacon wrote: > Adding Peter and Paul, > > On Sun, Feb 14, 2016 at 12:09:00PM +0300, Konstantin Khlebnikov wrote: > > bool atomic_add_max(atomic_t *var, int add, int max); > > bool atomic_sub_min(atomic_t *var, int sub, int min); > > What are the memory-ordering requirements for these? Do you also want > relaxed/acquire/release versions for the use-cases you outline? > > One observation is that you provide no ordering guarantees if the > comparison fails, which is fine if that's what you want, but we should > probably write that down like we do for cmpxchg. > > > bool this_cpu_add_max(var, add, max); > > bool this_cpu_sub_min(var, sub, min); > > > > They add/subtract only if result will be not bigger than max/lower that min. > > Returns true if operation was done and false otherwise. > > > > Inside they check that (add <= max - var) and (sub <= var - min). Signed > > operations work if all possible values fits into range which length fits > > into non-negative range of that type: 0..INT_MAX, INT_MIN+1..0, -1000..1000. > > Unsigned operations work if value always in valid range: min <= var <= max. > > Char and short automatically casts to int, they never overflows. > > > > Patch adds the same for atomic_long_t, atomic64_t, local_t, local64_t. > > And unsigned variants: atomic_u32_add_max atomic_u32_sub_min for atomic_t, > > atomic_u64_add_max atomic_u64_sub_min for atomic64_t. > > > > Patch comes with test which hopefully covers all possible cornercases, > > see CONFIG_ATOMIC64_SELFTEST and CONFIG_PERCPU_TEST. > > > > All this allows to build any kind of counter in several lines: > > Do you have another patch converting people over to these new atomics? The Changelog completely lacks a why. Why do we want this? -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
