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| author | Paolo Bonzini | 2018-02-16 10:05:23 +0100 |
|---|---|---|
| committer | Paolo Bonzini | 2018-03-12 16:12:47 +0100 |
| commit | a40161cbe9ccbcbab798c3e4d257c4bba99d153a (patch) | |
| tree | fe6cc9bb0a5a3253a59d0187a5266573a2b81e16 /include/qemu/sys_membarrier.h | |
| parent | membarrier: introduce qemu/sys_membarrier.h (diff) | |
| download | qemu-a40161cbe9ccbcbab798c3e4d257c4bba99d153a.tar.gz qemu-a40161cbe9ccbcbab798c3e4d257c4bba99d153a.tar.xz qemu-a40161cbe9ccbcbab798c3e4d257c4bba99d153a.zip | |
membarrier: add --enable-membarrier
Actually enable the global memory barriers if supported by the OS.
Because only recent versions of Linux include the support, they
are disabled by default. Note that it also has to be disabled
for QEMU to run under Wine.
Before this patch, rcutorture reports 85 ns/read for my machine,
after the patch it reports 12.5 ns/read. On the other hand updates
go from 50 *micro*seconds to 20 *milli*seconds.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'include/qemu/sys_membarrier.h')
| -rw-r--r-- | include/qemu/sys_membarrier.h | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/include/qemu/sys_membarrier.h b/include/qemu/sys_membarrier.h index 9ce7f5210b..316e3dc4a2 100644 --- a/include/qemu/sys_membarrier.h +++ b/include/qemu/sys_membarrier.h @@ -9,9 +9,19 @@ #ifndef QEMU_SYS_MEMBARRIER_H #define QEMU_SYS_MEMBARRIER_H 1 +#ifdef CONFIG_MEMBARRIER +/* Only block reordering at the compiler level in the performance-critical + * side. The slow side forces processor-level ordering on all other cores + * through a system call. + */ +extern void smp_mb_global_init(void); +extern void smp_mb_global(void); +#define smp_mb_placeholder() barrier() +#else /* Keep it simple, execute a real memory barrier on both sides. */ static inline void smp_mb_global_init(void) {} #define smp_mb_global() smp_mb() #define smp_mb_placeholder() smp_mb() +#endif #endif |