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[Qemu-devel] [PATCH v3 23/29] bitmap: add atomic set functions
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH v3 23/29] bitmap: add atomic set functions |
Date: |
Tue, 26 May 2015 18:54:59 +0200 |
From: Stefan Hajnoczi <address@hidden>
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 <address@hidden>
Message-Id: <address@hidden>
[Avoid barrier in the single word case, use full barrier instead of write.
- Paolo]
Signed-off-by: Paolo Bonzini <address@hidden>
---
include/qemu/bitmap.h | 2 ++
include/qemu/bitops.h | 14 ++++++++++++++
util/bitmap.c | 38 ++++++++++++++++++++++++++++++++++++++
3 files changed, 54 insertions(+)
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
diff --git a/util/bitmap.c b/util/bitmap.c
index 9c6bb52..39994af 100644
--- a/util/bitmap.c
+++ b/util/bitmap.c
@@ -11,6 +11,7 @@
#include "qemu/bitops.h"
#include "qemu/bitmap.h"
+#include "qemu/atomic.h"
/*
* bitmaps provide an array of bits, implemented using an an
@@ -177,6 +178,43 @@ void bitmap_set(unsigned long *map, long start, long nr)
}
}
+void bitmap_set_atomic(unsigned long *map, long start, long nr)
+{
+ unsigned long *p = map + BIT_WORD(start);
+ const long size = start + nr;
+ int bits_to_set = BITS_PER_LONG - (start % BITS_PER_LONG);
+ unsigned long mask_to_set = BITMAP_FIRST_WORD_MASK(start);
+
+ /* First word */
+ if (nr - bits_to_set > 0) {
+ atomic_or(p, mask_to_set);
+ nr -= bits_to_set;
+ bits_to_set = BITS_PER_LONG;
+ mask_to_set = ~0UL;
+ p++;
+ }
+
+ /* Full words */
+ if (bits_to_set == BITS_PER_LONG) {
+ while (nr >= BITS_PER_LONG) {
+ *p = ~0UL;
+ nr -= BITS_PER_LONG;
+ p++;
+ }
+ }
+
+ /* Last word */
+ if (nr) {
+ mask_to_set &= BITMAP_LAST_WORD_MASK(size);
+ atomic_or(p, mask_to_set);
+ } else {
+ /* If we avoided the full barrier in atomic_or(), issue a
+ * barrier to account for the assignments in the while loop.
+ */
+ smp_mb();
+ }
+}
+
void bitmap_clear(unsigned long *map, long start, long nr)
{
unsigned long *p = map + BIT_WORD(start);
--
1.8.3.1
- [Qemu-devel] [PATCH v3 18/29] translate-all: make less of tb_invalidate_phys_page_range depend on is_cpu_write_access, (continued)
- [Qemu-devel] [PATCH v3 18/29] translate-all: make less of tb_invalidate_phys_page_range depend on is_cpu_write_access, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 20/29] exec: invert return value of cpu_physical_memory_get_clean, rename, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 10/29] kvm: accept non-mapped memory in kvm_dirty_pages_log_change, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 13/29] ram_addr: tweaks to xen_modified_memory, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 09/29] memory: track DIRTY_MEMORY_CODE in mr->dirty_log_mask, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 22/29] memory: do not touch code dirty bitmap unless TCG is enabled, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 05/29] memory: differentiate memory_region_is_logging and memory_region_get_dirty_log_mask, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 04/29] display: add memory_region_sync_dirty_bitmap calls, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 15/29] exec: move functions to translate-all.h, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 23/29] bitmap: add atomic set functions,
Paolo Bonzini <=
- [Qemu-devel] [PATCH v3 19/29] exec: pass client mask to cpu_physical_memory_set_dirty_range, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 07/29] framebuffer: check memory_region_is_logging, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 11/29] memory: include DIRTY_MEMORY_MIGRATION in the dirty log mask, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 16/29] translate-all: remove unnecessary argument to tb_invalidate_phys_range, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 21/29] exec: only check relevant bitmaps for cleanliness, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 24/29] bitmap: add atomic test and clear, Paolo Bonzini, 2015/05/26