From 36546e5b803f6e363906607307f27c489441fd15 Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Tue, 2 Dec 2014 11:23:15 +0000 Subject: [PATCH] bitmap: add atomic test and clear The new bitmap_test_and_clear_atomic() function clears a range and returns whether or not the bits were set. Signed-off-by: Stefan Hajnoczi Message-Id: <1417519399-3166-3-git-send-email-stefanha@redhat.com> [Test before xchg; then a full barrier is needed at the end just like in the previous patch. The barrier can be avoided if we did at least one xchg. - Paolo] Reviewed-by: Fam Zheng Signed-off-by: Paolo Bonzini --- include/qemu/bitmap.h | 2 ++ util/bitmap.c | 45 +++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 47 insertions(+) diff --git a/include/qemu/bitmap.h b/include/qemu/bitmap.h index 3e0a4f3e0c..86dd9cd5fc 100644 --- a/include/qemu/bitmap.h +++ b/include/qemu/bitmap.h @@ -41,6 +41,7 @@ * 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_test_and_clear_atomic(dst, pos, nbits) Test and clear area * bitmap_find_next_zero_area(buf, len, pos, n, mask) Find bit free area */ @@ -229,6 +230,7 @@ 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); +bool bitmap_test_and_clear_atomic(unsigned long *map, long start, long nr); unsigned long bitmap_find_next_zero_area(unsigned long *map, unsigned long size, unsigned long start, diff --git a/util/bitmap.c b/util/bitmap.c index 39994af675..300a68e38c 100644 --- a/util/bitmap.c +++ b/util/bitmap.c @@ -235,6 +235,51 @@ void bitmap_clear(unsigned long *map, long start, long nr) } } +bool bitmap_test_and_clear_atomic(unsigned long *map, long start, long nr) +{ + unsigned long *p = map + BIT_WORD(start); + const long size = start + nr; + int bits_to_clear = BITS_PER_LONG - (start % BITS_PER_LONG); + unsigned long mask_to_clear = BITMAP_FIRST_WORD_MASK(start); + unsigned long dirty = 0; + unsigned long old_bits; + + /* First word */ + if (nr - bits_to_clear > 0) { + old_bits = atomic_fetch_and(p, ~mask_to_clear); + dirty |= old_bits & mask_to_clear; + nr -= bits_to_clear; + bits_to_clear = BITS_PER_LONG; + mask_to_clear = ~0UL; + p++; + } + + /* Full words */ + if (bits_to_clear == BITS_PER_LONG) { + while (nr >= BITS_PER_LONG) { + if (*p) { + old_bits = atomic_xchg(p, 0); + dirty |= old_bits; + } + nr -= BITS_PER_LONG; + p++; + } + } + + /* Last word */ + if (nr) { + mask_to_clear &= BITMAP_LAST_WORD_MASK(size); + old_bits = atomic_fetch_and(p, ~mask_to_clear); + dirty |= old_bits & mask_to_clear; + } else { + if (!dirty) { + smp_mb(); + } + } + + return dirty != 0; +} + #define ALIGN_MASK(x,mask) (((x)+(mask))&~(mask)) /**