On Sat, 3 Nov 2012, Paul E. McKenney wrote: > OK, I do understand why it happens to work. My question is instead why > it is considered a good idea. After all, it is the ->rda field that is > marked __percpu, not the ->mynode field. So in the interest of > mechanical checking and general readability, it seems to me that it > would be way better to apply __this_cpu_read() to rsp->rda rather than > to rsp->rda->mynode.
mynode is part of the structure reached via rda. Use on rsp->rda does not work since the offset of mynode must be added to rda before a fetch related to the current cpus per cpu address can be done. this_cpu_ptr relocates and address. this_cpu_read() relocates the address and performs the fetch. If you want to operate on rda then you can only use this_cpu_ptr. this_cpu_read() saves you more instructions since it can do the relocation and the fetch in one instruction. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
