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| author | Emilio G. Cota <cota@braap.org> | 2016-05-24 16:06:14 -0400 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2016-05-29 09:11:11 +0200 |
| commit | 15487aa132109891482f79d78a30d6cfd465a391 (patch) | |
| tree | c4f272a7dce759a217247f5e9a25b166a5977dd1 /docs | |
| parent | c983895258a771f8a5e4a53950bfb7fd2216651c (diff) | |
| download | qemu-15487aa132109891482f79d78a30d6cfd465a391.zip qemu-15487aa132109891482f79d78a30d6cfd465a391.tar.gz qemu-15487aa132109891482f79d78a30d6cfd465a391.tar.bz2 | |
atomics: do not emit consume barrier for atomic_rcu_read
Currently we emit a consume-load in atomic_rcu_read. Because of
limitations in current compilers, this is overkill for non-Alpha hosts
and it is only useful to make Thread Sanitizer work.
This patch leaves the consume-load in atomic_rcu_read when
compiling with Thread Sanitizer enabled, and resorts to a
relaxed load + smp_read_barrier_depends otherwise.
On an RMO host architecture, such as aarch64, the performance
improvement of this change is easily measurable. For instance,
qht-bench performs an atomic_rcu_read on every lookup. Performance
before and after applying this patch:
$ tests/qht-bench -d 5 -n 1
Before: 9.78 MT/s
After: 10.96 MT/s
Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <1464120374-8950-4-git-send-email-cota@braap.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'docs')
0 files changed, 0 insertions, 0 deletions