On Wednesday 10 May 2006 00:56, Christoph Lameter wrote: > On Tue, 9 May 2006, Chris Wright wrote: > > > Add "always lock'd" implementations of set_bit, clear_bit and > > change_bit and the corresponding test_and_ functions. Also add > > "always lock'd" implementation of cmpxchg. These give guaranteed > > strong synchronisation and are required for non-SMP kernels running on > > an SMP hypervisor. > > Could you explain why this is done and what is exactly meant with "always > looked"? Wh the performance impact? When UP guest runs on SMP hypervisor they still need the LOCK prefix to talk to the hypervisor through shared memory in a smp safe way. Normally UP kernels don't use any LOCK prefixes. I suggested to refactor the bitops this way earlier for this. -Andi
