Commit Graph

5 Commits

Author SHA1 Message Date
Jan Beulich cb8095bba6 x86: atomic64 assembly improvements
In the "xchg" implementation, %ebx and %ecx don't need to be copied
into %eax and %edx respectively (this is only necessary when desiring
to only read the stored value).

In the "add_unless" implementation, swapping the use of %ecx and %esi
for passing arguments allows %esi to become an input only (i.e.
permitting the register to be re-used to address the same object
without reload).

In "{add,sub}_return", doing the initial read64 through the passed in
%ecx decreases a register dependency.

In "inc_not_zero", a branch can be eliminated by or-ing together the
two halves of the current (64-bit) value, and code size can be further
reduced by adjusting the arithmetic slightly.

v2: Undo the folding of "xchg" and "set".

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Link: http://lkml.kernel.org/r/4F19A2BC020000780006E0DC@nat28.tlf.novell.com
Cc: Luca Barbieri <luca@luca-barbieri.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
2012-01-20 17:29:49 -08:00
Jan Beulich 60cf637a13 x86: Use {push,pop}_cfi in more places
Cleaning up and shortening code...

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Cc: Alexander van Heukelum <heukelum@fastmail.fm>
LKML-Reference: <4D6BD35002000078000341DA@vpn.id2.novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-02-28 18:06:22 +01:00
Luca Barbieri f3e8313146 x86-32: Fix atomic64_inc_not_zero return value convention
atomic64_inc_not_zero must return 1 if it perfomed the add and 0 otherwise.
It was doing the opposite thing.

Signed-off-by: Luca Barbieri <luca@luca-barbieri.com>
LKML-Reference: <1267469749-11878-6-git-send-email-luca@luca-barbieri.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
2010-03-01 11:39:03 -08:00
Luca Barbieri 6e6104fe08 x86-32: Fix atomic64_add_unless return value convention
atomic64_add_unless must return 1 if it perfomed the add and 0 otherwise.
The implementation did the opposite thing.

Reported-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Luca Barbieri <luca@luca-barbieri.com>
LKML-Reference: <1267469749-11878-3-git-send-email-luca@luca-barbieri.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
2010-03-01 11:38:46 -08:00
Luca Barbieri a7e926abc3 x86-32: Rewrite 32-bit atomic64 functions in assembly
This patch replaces atomic64_32.c with two assembly implementations,
one for 386/486 machines using pushf/cli/popf and one for 586+ machines
using cmpxchg8b.

The cmpxchg8b implementation provides the following advantages over the
current one:

1. Implements atomic64_add_unless, atomic64_dec_if_positive and
   atomic64_inc_not_zero

2. Uses the ZF flag changed by cmpxchg8b instead of doing a comparison

3. Uses custom register calling conventions that reduce or eliminate
   register moves to suit cmpxchg8b

4. Reads the initial value instead of using cmpxchg8b to do that.
   Currently we use lock xaddl and movl, which seems the fastest.

5. Does not use the lock prefix for atomic64_set
   64-bit writes are already atomic, so we don't need that.
   We still need it for atomic64_read to avoid restoring a value
   changed in the meantime.

6. Allocates registers as well or better than gcc

The 386 implementation provides support for 386 and 486 machines.
386/486 SMP is not supported (we dropped it), but such support can be
added easily if desired.

A pure assembly implementation is required due to the custom calling
conventions, and desire to use %ebp in atomic64_add_return (we need
7 registers...), as well as the ability to use pushf/popf in the 386
code without an intermediate pop/push.

The parameter names are changed to match the convention in atomic_64.h

Changes in v3 (due to rebasing to tip/x86/asm):
- Patches atomic64_32.h instead of atomic_32.h
- Uses the CALL alternative mechanism from commit
  1b1d925818

Changes in v2:
- Merged 386 and cx8 support in the same patch
- 386 support now done in assembly, C code no longer used at all
- cmpxchg64 is used for atomic64_cmpxchg
- stop using macros, use one-line inline functions instead
- miscellanous changes and improvements

Signed-off-by: Luca Barbieri <luca@luca-barbieri.com>
LKML-Reference: <1267005265-27958-5-git-send-email-luca@luca-barbieri.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
2010-02-25 20:47:30 -08:00