Messages in this thread | | | From | Dexuan Cui <> | Subject | RE: sync_set_bit() vs set_bit() -- what's the difference? | Date | Wed, 27 Aug 2014 07:50:52 +0000 |
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> -----Original Message----- > From: Jan Beulich > Sent: Wednesday, August 27, 2014 15:39 PM > >>> On 27.08.14 at 09:30, <decui@microsoft.com> wrote: > > I'm curious about the difference. :-) > > > > sync_set_bit() is only used in drivers/hv/ and drivers/xen/ while set_bit() > > is used in all other places. What makes hv/xen special? > > I guess this would really want to be used by anything communicating > with a hypervisor or a remote driver: set_bit() gets its LOCK prefix > discarded when the local kernel determines it runs on a single CPU > only. Obviously having knowledge of the CPU count inside a VM does > not imply anything about the number of CPUs available to the host, > i.e. stripping LOCK prefixes in that case would be unsafe. > > Jan
Thank you, Juergen and Jan for your quick answers!
I didn't realize LOCK_PREFIX is "" for UP. :-)
Thanks, -- Dexuan
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