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| author | Stefan Hajnoczi <stefanha@redhat.com> | 2014-12-02 11:23:14 +0000 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2015-06-05 17:10:00 +0200 |
| commit | 9f02cfc84b85929947b32fe1674fbc6a429f332a (patch) | |
| tree | 75a66020271291432bf06bc7db7af66a37de5c9a /include/qemu | |
| parent | 9460dee4b2258e3990906fb34099481c8334c267 (diff) | |
| download | hqemu-9f02cfc84b85929947b32fe1674fbc6a429f332a.zip hqemu-9f02cfc84b85929947b32fe1674fbc6a429f332a.tar.gz | |
bitmap: add atomic set functions
Use atomic_or() for atomic bitmaps where several threads may set bits at
the same time. This avoids the race condition between threads loading
an element, bitwise ORing, and then storing the element.
When setting all bits in a word we can avoid atomic ops and instead just
use an smp_mb() at the end.
Most bitmap users don't need atomicity so introduce new functions.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <1417519399-3166-2-git-send-email-stefanha@redhat.com>
[Avoid barrier in the single word case, use full barrier instead of write.
- Paolo]
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'include/qemu')
| -rw-r--r-- | include/qemu/bitmap.h | 2 | ||||
| -rw-r--r-- | include/qemu/bitops.h | 14 |
2 files changed, 16 insertions, 0 deletions
diff --git a/include/qemu/bitmap.h b/include/qemu/bitmap.h index f0273c9..3e0a4f3 100644 --- a/include/qemu/bitmap.h +++ b/include/qemu/bitmap.h @@ -39,6 +39,7 @@ * bitmap_empty(src, nbits) Are all bits zero in *src? * bitmap_full(src, nbits) Are all bits set in *src? * bitmap_set(dst, pos, nbits) Set specified bit area + * bitmap_set_atomic(dst, pos, nbits) Set specified bit area with atomic ops * bitmap_clear(dst, pos, nbits) Clear specified bit area * bitmap_find_next_zero_area(buf, len, pos, n, mask) Find bit free area */ @@ -226,6 +227,7 @@ static inline int bitmap_intersects(const unsigned long *src1, } void bitmap_set(unsigned long *map, long i, long len); +void bitmap_set_atomic(unsigned long *map, long i, long len); void bitmap_clear(unsigned long *map, long start, long nr); unsigned long bitmap_find_next_zero_area(unsigned long *map, unsigned long size, diff --git a/include/qemu/bitops.h b/include/qemu/bitops.h index 8abdcf9..8164225 100644 --- a/include/qemu/bitops.h +++ b/include/qemu/bitops.h @@ -16,6 +16,7 @@ #include <assert.h> #include "host-utils.h" +#include "atomic.h" #define BITS_PER_BYTE CHAR_BIT #define BITS_PER_LONG (sizeof (unsigned long) * BITS_PER_BYTE) @@ -39,6 +40,19 @@ static inline void set_bit(long nr, unsigned long *addr) } /** + * set_bit_atomic - Set a bit in memory atomically + * @nr: the bit to set + * @addr: the address to start counting from + */ +static inline void set_bit_atomic(long nr, unsigned long *addr) +{ + unsigned long mask = BIT_MASK(nr); + unsigned long *p = addr + BIT_WORD(nr); + + atomic_or(p, mask); +} + +/** * clear_bit - Clears a bit in memory * @nr: Bit to clear * @addr: Address to start counting from |
