Messages in this thread | | | From | Andi Kleen <> | Subject | Re: [RFC PATCH 05/35] Add sync bitops | Date | Wed, 10 May 2006 01:04:34 +0200 |
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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
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