On Wed, Oct 11, 2017 at 05:07:05PM +0100, David Howells wrote: > Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > > > It does not. In most cases, the barriered version would be > > smp_store_release(). > > Ummm... Is that good enough? Is: > > WRITE_ONCE(x, 1); > WRITE_ONCE(x, 2); > > equivalent to: > > smp_store_release(x, 1); > smp_store_release(x, 2); > > if CONFIG_SMP=n? smp_store_release(&x, 1); smp_store_release(&x, 2); But yes, give or take that smp_store_release() potentially disables more compiler optimizations than does WRITE_ONCE(). > (Consider what happens if an interrupt messes with x). OK, I will bite... What is your scenario in which an interrupt gives different results for CONFIG_SMP=n? The barriers > If it is good enough, should we be using smp_load_acquire() rather than > READ_ONCE()? On x86, that might be OK, give or take that smp_load_acquire() potentially disables more optimizations than does READ_ONCE(). But on ARM, PowerPC, MIPS, and so on, smp_load_acquire() emits a memory-barrier instruction and READ_ONCE() does not. Thanx, Paul
