Re: [PATCH] bitops: add _local bitops
From: Rob Landley
Date: Thu May 10 2012 - 13:38:18 EST
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>
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-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/