On 09/03/09 20:35, H. Peter Anvin wrote: > On 09/03/2009 07:59 PM, Tejun Heo wrote: > >> Another question. Other than saving and loading an extra segment >> register on kernel entry/exit, whether using the same or different >> segment registers doesn't look like would make difference >> performance-wise. If I'm interpreting the wording in the optimization >> manual correctly, it means that each non-zero segment based memory >> access will be costly regardless of which specific segment register is >> in use and there's no way we can merge segment based dereferences for >> stackprotector and percpu variables. >> >> > It's correct that it doesn't make any difference for access, only for load. > Well, to be completely precise, restore. When returning to usermode, the "pop %seg" is slightly faster if you're restoring a null selector, which is typically the case for %fs as 32-bit usermode doesn't use it. J -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html