| Message ID | 20190430034412.12935-4-richardw.yang@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Cleanup migration/ram.c | expand |
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 <richardw.yang@linux.intel.com> 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(); >
On Wed, Jul 17, 2019 at 11:17:50AM +0200, Paolo Bonzini wrote: >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 <richardw.yang@linux.intel.com> > >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. > Thanks, then I would leave current code untouched. >Paolo >
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();
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 <richardw.yang@linux.intel.com> --- include/exec/ram_addr.h | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-)