diff options
| author | Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> | 2016-01-25 16:33:20 -0500 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2016-02-09 14:50:16 +0100 |
| commit | fed0764fafd8e2e629a033c0f7df4106b0dcb7f0 (patch) | |
| tree | 11877084d79ccadb090b726cb280bb76e72ca4aa /include/linux/compiler.h | |
| parent | 06bea3dbfe6a4c333c4333362c46bdf4d9e43504 (diff) | |
| download | op-kernel-dev-fed0764fafd8e2e629a033c0f7df4106b0dcb7f0.zip op-kernel-dev-fed0764fafd8e2e629a033c0f7df4106b0dcb7f0.tar.gz | |
locking/atomics: Update comment about READ_ONCE() and structures
The comment is out of data. Also point out the performance drawback
of the barrier();__builtin_memcpy(); barrier() followed by another
copy from stack (__u) to lvalue;
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1453757600-11441-1-git-send-email-konrad.wilk@oracle.com
[ Made it a bit more readable. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux/compiler.h')
| -rw-r--r-- | include/linux/compiler.h | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 00b042c..4291592 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -263,8 +263,9 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s * In contrast to ACCESS_ONCE these two macros will also work on aggregate * data types like structs or unions. If the size of the accessed data * type exceeds the word size of the machine (e.g., 32 bits or 64 bits) - * READ_ONCE() and WRITE_ONCE() will fall back to memcpy and print a - * compile-time warning. + * READ_ONCE() and WRITE_ONCE() will fall back to memcpy(). There's at + * least two memcpy()s: one for the __builtin_memcpy() and then one for + * the macro doing the copy of variable - '__u' allocated on the stack. * * Their two major use cases are: (1) Mediating communication between * process-level code and irq/NMI handlers, all running on the same CPU, |
