Messages in this thread | | | Subject | Re: [PATCH] Futexes IV (Fast Lightweight Userspace Semaphores) | Date | Fri, 8 Mar 2002 23:36:01 +0000 (GMT) | From | Alan Cox <> |
| |
> > It's not just 386 vs later due to cmpxchg. It's also the simple issue of > > UP vs SMP - a UP system still wants to do locking, but it doesn't need the > > lock prefix. And that lock prefix makes a _huge_ difference > > performance-wise. > > Fail to see why that matters. User level locking is mostly beneficial on SMPs. > So, you lock the bus for the atomic update. This is UP, nothing's going on > on the bus anyway.
Lots of older x86 is too stupid to optimise exclusive cache line locked operations. After all the bus is still shared - PCI bus masters for one
Alan - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |