On Thu, 03/26 18:38, Paolo Bonzini wrote:
> From: Stefan Hajnoczi <stefa...@redhat.com>
>
> 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 <stefa...@redhat.com>
> Message-Id: <1417519399-3166-3-git-send-email-stefa...@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]
>
> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
> ---
> include/qemu/bitmap.h | 2 ++
> util/bitmap.c | 43 +++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 45 insertions(+)
>
> diff --git a/include/qemu/bitmap.h b/include/qemu/bitmap.h
> index 3e0a4f3..86dd9cd 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 e4957da..570758a 100644
> --- a/util/bitmap.c
> +++ b/util/bitmap.c
> @@ -232,6 +232,49 @@ 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 */
> + while (nr - bits_to_clear >= 0) {
> + if (*p) {
> + old_bits = atomic_xchg(p, 0);
> + dirty |= old_bits;
> + }
> + nr -= bits_to_clear;
> + 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();
Is this for the "*p" in the while loop? If so, and if the while loop is not
executed (bits contained in the first word, and clean), isn't this barrier
superfluous then?
Fam
> + }
> + }
> +
> + return dirty;
> +}
> +
> #define ALIGN_MASK(x,mask) (((x)+(mask))&~(mask))
>
> /**
> --
> 2.3.3
>
>
>
