Commit Graph

7 Commits

Author SHA1 Message Date
Paolo Bonzini 803cf26a9e atomic: base mb_read/mb_set on load-acquire and store-release
This introduces load-acquire and store-release operations in QEMU.
For now, just use them as an implementation detail of atomic_mb_read
and atomic_mb_set.

Since docs/atomics.txt documents that atomic_mb_read only synchronizes
with an atomic_mb_set of the same variable, we can use the new implementation
everywhere instead of seq-cst loads and stores.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2016-10-24 15:27:15 +02:00
Paolo Bonzini f1ee86963b atomic: introduce smp_mb_acquire and smp_mb_release
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2016-10-24 11:30:55 +02:00
Paolo Bonzini a4a0e4b258 docs/atomics: update comparison with Linux
Over time, some differences between QEMU and Linux atomics are getting
smoothed.  In particular, Linux grew atomic_fetch_or (and in general
the differences regarding RMW operations were not described accurately)
and smp_load_acquire/smp_store_release.  Also, set_mb was renamed to
smp_store_mb().  Include these changes in the documentation.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2016-05-29 09:11:11 +02:00
Emilio G. Cota 56ebe02203 docs/atomics: update atomic_read/set comparison with Linux
Recently Linux did a mass conversion of its atomic_read/set calls
so that they at least are READ/WRITE_ONCE. See Linux's commit
62e8a325 ("atomic, arch: Audit atomic_{read,set}()"). It seems though
that their documentation hasn't been updated to reflect this.

The appended updates our documentation to reflect the change, which
means there is effectively no difference between our atomic_read/set
and the current Linux implementation.

While at it, fix the statement that a barrier is implied by
atomic_read/set, which is incorrect. Volatile/atomic semantics prevent
transformations pertaining the variable they apply to; this, however,
has no effect on surrounding statements like barriers do. For more
details on this, see:
  https://gcc.gnu.org/onlinedocs/gcc/Volatiles.html

Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <1464120374-8950-2-git-send-email-cota@braap.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2016-05-29 09:11:11 +02:00
Pranith Kumar dfc007f7f7 docs/atomics.txt: Update pointer to linux macro
Add a missing end brace and update doc to point to the latest access
macro. ACCESS_ONCE() is deprecated.

Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Message-Id: <1462198852-28694-1-git-send-email-bobby.prani@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2016-05-23 16:53:43 +02:00
Laszlo Ersek d3e4abdddf docs/atomics.txt: fix two typos
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
2015-04-30 16:05:48 +03:00
Paolo Bonzini 5444e768ee add a header file for atomic operations
We're already using them in several places, but __sync builtins are just
too ugly to type, and do not provide seqcst load/store operations.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2013-07-04 17:42:49 +02:00