1. 02 3月, 2010 2 次提交
  2. 26 2月, 2010 1 次提交
    • L
      x86-32: Rewrite 32-bit atomic64 functions in assembly · a7e926ab
      Luca Barbieri 提交于
      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
        1b1d9258
      
      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: NLuca Barbieri <luca@luca-barbieri.com>
      LKML-Reference: <1267005265-27958-5-git-send-email-luca@luca-barbieri.com>
      Signed-off-by: NH. Peter Anvin <hpa@zytor.com>
      a7e926ab
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