motorhead/qemu
1
0
Fork 0
mirror of https://github.com/Motorhead1991/qemu.git synced 2025-08-22 09:32:40 -06:00
Code Issues Projects Releases Packages Wiki Activity Actions

bitmap: add atomic set functions

Browse source 
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>
This commit is contained in:
Stefan Hajnoczi 2014-12-02 11:23:14 +00:00 • committed by Paolo Bonzini
parent 9460dee4b2
commit 9f02cfc84b
3 changed files with 54 additions and 0 deletions
Download patch file Download diff file Expand all files Collapse all files

14
include/qemu/bitops.h
View file

@ -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)
@ -38,6 +39,19 @@ static inline void set_bit(long nr, unsigned long *addr)
*p |= mask;
}
/**
* 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