[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 2/3] xen/atomic: Implement atomic_{inc, dec}_bounded()
On 02/07/14 15:05, Jan Beulich wrote: >>>> On 02.07.14 at 15:47, <andrew.cooper3@xxxxxxxxxx> wrote: >> These will increment/decremented an atomic_t, while ensuring that the >> atomic_t >> doesn't hit a specific bound. >> >> This involves introducing atomic_cmpxchg() for x86, which previously only >> existed on ARM. >> >> Suggested-by: Don Slutz <dslutz@xxxxxxxxxxx> >> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> >> CC: Keir Fraser <keir@xxxxxxx> >> CC: Jan Beulich <JBeulich@xxxxxxxx> > You should be getting used to Cc all "REST" maintainers on respective > changes. Oops yes - I will see about updating my auto-cc list hooks. > >> --- /dev/null >> +++ b/xen/common/atomic.c >> @@ -0,0 +1,35 @@ >> +#include <xen/atomic.h> >> + >> +bool_t atomic_inc_bounded(atomic_t *v, int bound) >> +{ >> + int old, new, prev = atomic_read(v); >> + >> + do >> + { >> + old = prev; >> + new = old + 1; >> + if ( new >= bound ) >> + return 0; >> + >> + prev = atomic_cmpxchg(v, old, new); >> + } while ( prev != old ); >> + >> + return 1; >> +} >> + >> +bool_t atomic_dec_bounded(atomic_t *v, int bound) >> +{ >> + int old, new, prev = atomic_read(v); >> + >> + do >> + { >> + old = prev; >> + new = old - 1; >> + if ( new <= bound ) >> + return 0; >> + >> + prev = atomic_cmpxchg(v, old, new); >> + } while ( prev != old ); >> + >> + return 1; >> +} > Same question here: Do we really need these? There are various uses > of cmpxchg() in common code already, and in patch 3 you don't really > need the cmpxchg to happen on an atomic_t, so plain cmpxchg() with > the little bit of extra logic open coded would seem fine to me. > > Jan > These as in atomic_{inc,dec}_bounded() ? They logically fit alongside atomic_{inc,dec}_and_test(), and I came to the conclusion that they would likely be useful elsewhere. I realise that these are not fantastic reasons alone... ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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