* [email protected] <[email protected]> wrote:
> From: Vincent Donnefort <[email protected]> > > Introducing two macro helpers u64_32read() and u64_32read_set_copy() to > factorize the u64 vminruntime and last_update_time read on a 32-bits > architecture. Those new helpers encapsulate smp_rmb() and smp_wmb() > synchronization and therefore, have a small penalty in set_task_rq_fair() > and init_cfs_rq(). > > The choice of using a macro over an inline function is driven by the > conditional u64 variable copy declarations. Could you please explain how "conditional u64 variable copy declarations" prevents us to use an inline function for this: > +/* > + * u64_32read() / u64_32read_set_copy() > + * > + * Use the copied u64 value to protect against data race. This is only > + * applicable for 32-bits architectures. > + */ > +#if !defined(CONFIG_64BIT) && defined(CONFIG_SMP) > +# define u64_32read(val, copy) > \ > +({ \ > + u64 _val; \ > + u64 _val_copy; \ > + \ > + do { \ > + _val_copy = copy; \ > + /* \ > + * paired with u64_32read_set_copy, ordering access \ > + * to val and copy. \ > + */ \ > + smp_rmb(); \ > + _val = val; \ > + } while (_val != _val_copy); \ > + \ > + _val; \ > +}) > +# define u64_32read_set_copy(val, copy) > \ > +do { \ > + /* paired with u64_32read, ordering access to val and copy */ \ > + smp_wmb(); \ > + copy = val; \ > +} while (0) > +#else > +# define u64_32read(val, copy) (val) > +# define u64_32read_set_copy(val, copy) do { } while (0) > +#endif > + Thanks, Ingo
