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Re: [Qemu-devel] [PATCH 3/3] ram: RAMBlock->offset is always aligned to
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 3/3] ram: RAMBlock->offset is always aligned to a word |
Date: |
Wed, 17 Jul 2019 11:17:50 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 |
On 30/04/19 05:44, Wei Yang wrote:
> RAMBlock->offset is calculated by find_ram_offset, which makes sure the
> offset is aligned to a word.
>
> This patch removes the alignment check on offset and unnecessary
> variable *word*.
>
> Signed-off-by: Wei Yang <address@hidden>
I would add an assertion instead, but overall leaving the condition
there is harmless. You still need the "else" part for the case where
the length is unaligned.
Paolo
> ---
> include/exec/ram_addr.h | 15 +++++++++------
> 1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> index 3dfb2d52fb..a7c81bdb32 100644
> --- a/include/exec/ram_addr.h
> +++ b/include/exec/ram_addr.h
> @@ -413,18 +413,21 @@ uint64_t cpu_physical_memory_sync_dirty_bitmap(RAMBlock
> *rb,
> uint64_t *real_dirty_pages)
> {
> ram_addr_t addr;
> - unsigned long word = BIT_WORD(rb->offset >> TARGET_PAGE_BITS);
> uint64_t num_dirty = 0;
> unsigned long *dest = rb->bmap;
>
> - /* offset and length is aligned at the start of a word? */
> - if (((word * BITS_PER_LONG) << TARGET_PAGE_BITS) == (rb->offset) &&
> - !(length & ((BITS_PER_LONG << TARGET_PAGE_BITS) - 1))) {
> + /*
> + * Since RAMBlock->offset is guaranteed to be aligned to a word by
> + * find_ram_offset(), if length is aligned at the start of a word, go the
> + * fast path.
> + */
> + if (!(length & ((BITS_PER_LONG << TARGET_PAGE_BITS) - 1))) {
> int k;
> int nr = BITS_TO_LONGS(length >> TARGET_PAGE_BITS);
> unsigned long * const *src;
> - unsigned long idx = (word * BITS_PER_LONG) / DIRTY_MEMORY_BLOCK_SIZE;
> - unsigned long offset = BIT_WORD((word * BITS_PER_LONG) %
> + unsigned long idx = (rb->offset >> TARGET_PAGE_BITS) /
> + DIRTY_MEMORY_BLOCK_SIZE;
> + unsigned long offset = BIT_WORD((rb->offset >> TARGET_PAGE_BITS) %
> DIRTY_MEMORY_BLOCK_SIZE);
>
> rcu_read_lock();
>
- Re: [Qemu-devel] [PATCH 3/3] ram: RAMBlock->offset is always aligned to a word,
Paolo Bonzini <=