On Wed, May 09, 2012 at 07:03:37AM -0700, H. Peter Anvin wrote: > On 05/09/2012 06:45 AM, Michael S. Tsirkin wrote: > > kvm needs to update some hypervisor variables atomically > > in a sense that the operation can't be interrupted > > in the middle. However the hypervisor always runs > > on the same CPU so it does not need any memory > > barrier or lock prefix. > > > > At Peter Anvin's suggestion, add _local bitops for this purpose: > > define them as non-atomics for x86 and (for now) atomics > > for everyone else. > > > > Uses are not restricted to virtualization: they > > might be useful to communicate with an interrupt > > handler if we know that it's running on the same CPU. > > > > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > > I don't think you can use the x86 nonatomics as-is, because they don't > contain optimization barriers. > > -hpa By the way, clear_bit on x86 does not seem to contain an optimization barrier - is my reading correct? Lock prefix does not affect the compiler, right? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
