From: Fam Zheng <famz@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 17/22] bitmap: add atomic test and clear
Date: Fri, 27 Mar 2015 14:37:27 +0800 [thread overview]
Message-ID: <20150327063727.GC16079@ad.nay.redhat.com> (raw)
In-Reply-To: <1427391520-29497-18-git-send-email-pbonzini@redhat.com>
On Thu, 03/26 18:38, Paolo Bonzini wrote:
> From: Stefan Hajnoczi <stefanha@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 <stefanha@redhat.com>
> 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]
>
> Signed-off-by: Paolo Bonzini <pbonzini@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
>
>
>
next prev parent reply other threads:[~2015-03-27 6:37 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-26 17:38 [Qemu-devel] [PATCH 00/22] Dirty bitmap atomic access and optimizations Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 01/22] memory: add memory_region_ram_resize Paolo Bonzini
2015-03-28 18:58 ` Michael S. Tsirkin
2015-03-29 7:30 ` Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 02/22] acpi-build: remove dependency from ram_addr.h Paolo Bonzini
2015-03-28 18:58 ` Michael S. Tsirkin
2015-03-26 17:38 ` [Qemu-devel] [PATCH 03/22] memory: the only dirty memory flag for users is DIRTY_MEMORY_VGA Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 04/22] display: enable DIRTY_MEMORY_VGA tracking explicitly Paolo Bonzini
2015-04-20 13:11 ` Stefan Hajnoczi
2015-04-20 13:54 ` Paolo Bonzini
2015-04-22 9:12 ` Stefan Hajnoczi
2015-03-26 17:38 ` [Qemu-devel] [PATCH 05/22] memory: return bitmap from memory_region_is_logging Paolo Bonzini
2015-03-27 5:44 ` Fam Zheng
2015-03-27 6:01 ` Paolo Bonzini
2015-03-28 18:54 ` Michael S. Tsirkin
2015-03-29 7:33 ` Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 06/22] framebuffer: check memory_region_is_logging Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 07/22] ui/console: " Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 08/22] memory: track DIRTY_MEMORY_CODE in mr->dirty_log_mask Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 09/22] memory: return DIRTY_MEMORY_MIGRATION from memory_region_is_logging Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 10/22] ram_addr: tweaks to xen_modified_memory Paolo Bonzini
2015-03-28 19:04 ` Stefano Stabellini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 11/22] exec: simplify notdirty_mem_write Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 12/22] exec: use memory_region_is_logging to optimize dirty tracking Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 13/22] exec: pass client mask to cpu_physical_memory_set_dirty_range Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 14/22] exec: only check relevant bitmaps for cleanliness Paolo Bonzini
2015-03-27 6:10 ` Fam Zheng
2015-03-27 9:19 ` Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 15/22] memory: do not touch code dirty bitmap unless TCG is enabled Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 16/22] bitmap: add atomic set functions Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 17/22] bitmap: add atomic test and clear Paolo Bonzini
2015-03-27 6:37 ` Fam Zheng [this message]
2015-03-27 9:21 ` Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 18/22] memory: use atomic ops for setting dirty memory bits Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 19/22] migration: move dirty bitmap sync to ram_addr.h Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 20/22] memory: replace cpu_physical_memory_reset_dirty() with test-and-clear Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 21/22] memory: make cpu_physical_memory_sync_dirty_bitmap() fully atomic Paolo Bonzini
2015-03-26 17:38 ` [Qemu-devel] [PATCH 22/22] migration: run bitmap sync outside iothread lock Paolo Bonzini
2015-04-20 13:23 ` [Qemu-devel] [PATCH 00/22] Dirty bitmap atomic access and optimizations Stefan Hajnoczi
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