[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] ia64: introduce atomic_{read,write}NN()
>>> On 25.11.11 at 02:52, "KUWAMURA Shin'ya" <kuwa@xxxxxxxxxxxxxx> wrote: > Hi Jan, > > Excuse me for too late response. Thank you for your work. > But I have a question. > >>>>>> On Fri, 11 Nov 2011 16:09:25 +0000 >>>>>> JBeulich@xxxxxxxx("Jan Beulich") said: >> >> +#define build_atomic_read(tag, type) \ >> +static inline type atomic_read##tag(const volatile type *addr) \ >> +{ \ >> + type ret; \ >> + asm volatile("ld%2.acq %0 = %1" \ >> + : "=r" (ret) \ >> + : "m" (*addr), "i" (sizeof(type))); \ >> + return ret; \ >> +} >> + >> +#define build_atomic_write(tag, type) \ >> +static inline void atomic_write##tag(volatile type *addr, type val) \ >> +{ \ >> + asm volatile("st%2.rel %0 = %1" \ >> + : "=m" (*addr) \ >> + : "r" (val), "i" (sizeof(type))); \ >> +} > > Why do you use explicitly ld.acq and st.rel? > I think that volatile variables are always accessed using ld.acq and > st.rel and they are not required. That would imply the compiler would attach these completers, but in inline assembly it obviously can't. > For example, The implementation of Linux is as follows: > > #define atomic_read(v) (*(volatile int *)&(v)->counter) > #define atomic64_read(v) (*(volatile long *)&(v)->counter) Indeed - here the compiler is required to use acquire loads and release stores. The inline assembly has to mimic this behavior. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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