On 05/09/2012 08:45 AM, Michael S. Tsirkin wrote: > diff --git a/Documentation/atomic_ops.txt b/Documentation/atomic_ops.txt > index 27f2b21..b7e3b67 100644 > --- a/Documentation/atomic_ops.txt > +++ b/Documentation/atomic_ops.txt > @@ -520,6 +520,25 @@ The __clear_bit_unlock version is non-atomic, however it still implements > unlock barrier semantics. This can be useful if the lock itself is protecting > the other bits in the word. > > +Local versions of the bitmask operations are also provided. They are used in > +contexts where the operations need to be performed atomically with respect to > +the local CPU, but no other CPU accesses the bitmask. This assumption makes it > +possible to avoid the need for SMP protection and use less expensive atomic > +operations in the implementation. > +They have names similar to the above bitmask operation interfaces, > +except that _local is sufficed to the interface name. > + > + void set_bit_local(unsigned long nr, volatile unsigned long *addr); > + void clear_bit_local(unsigned long nr, volatile unsigned long *addr); > + void change_bit_local(unsigned long nr, volatile unsigned long *addr); > + int test_and_set_bit_local(unsigned long nr, volatile unsigned long *addr); > + int test_and_clear_bit_local(unsigned long nr, volatile unsigned long *addr); > + int test_and_change_bit_local(unsigned long nr, volatile unsigned long *addr); > + > +These local variants are useful for example if the bitmask may be accessed from > +a local intrerrupt, or from a hypervisor on the same CPU if running in a VM. > +These local variants also do not have any special memory barrier semantics. > + > Finally, there are non-atomic versions of the bitmask operations > provided. They are used in contexts where some other higher-level SMP > locking scheme is being used to protect the bitmask, and thus less For this bit: Acked-by: Rob Landley <rob@xxxxxxxxxxx> Rob -- GNU/Linux isn't: Linux=GPLv2, GNU=GPLv3+, they can't share code. Either it's "mere aggregation", or a license violation. Pick one. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
