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ram: optimize migration bitmap walking 

Instead of testing each page individually, we search what is the next
dirty page with a bitmap operation.  We have to reorganize the code to
move from a "for" loop, to a while(dirty) loop.

Signed-off-by: Juan Quintela <quintela@redhat.com>
This commit is contained in:
Juan Quintela 2012-10-18 00:00:59 +02:00
parent ece7931817
commit 4c8ae0f60e
1 changed files with 26 additions and 19 deletions
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45
arch_init.c
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@ -343,18 +343,21 @@ static unsigned long *migration_bitmap;
static uint64_t migration_dirty_pages;
static uint32_t last_version;
static inline bool migration_bitmap_test_and_reset_dirty(MemoryRegion *mr,
ram_addr_t offset)
static inline
ram_addr_t migration_bitmap_find_and_reset_dirty(MemoryRegion *mr,
ram_addr_t start)
{
bool ret;
int nr = (mr->ram_addr + offset) >> TARGET_PAGE_BITS;
unsigned long base = mr->ram_addr >> TARGET_PAGE_BITS;
unsigned long nr = base + (start >> TARGET_PAGE_BITS);
unsigned long size = base + (int128_get64(mr->size) >> TARGET_PAGE_BITS);
ret = test_and_clear_bit(nr, migration_bitmap);
unsigned long next = find_next_bit(migration_bitmap, size, nr);
if (ret) {
if (next < size) {
clear_bit(next, migration_bitmap);
migration_dirty_pages--;
}
return ret;
return (next - base) << TARGET_PAGE_BITS;
}
static inline bool migration_bitmap_set_dirty(MemoryRegion *mr,
@ -423,6 +426,7 @@ static int ram_save_block(QEMUFile *f, bool last_stage)
{
RAMBlock *block = last_seen_block;
ram_addr_t offset = last_offset;
bool complete_round = false;
int bytes_sent = -1;
MemoryRegion *mr;
ram_addr_t current_addr;
@ -430,9 +434,21 @@ static int ram_save_block(QEMUFile *f, bool last_stage)
if (!block)
block = QTAILQ_FIRST(&ram_list.blocks);
do {
while (true) {
mr = block->mr;
if (migration_bitmap_test_and_reset_dirty(mr, offset)) {
offset = migration_bitmap_find_and_reset_dirty(mr, offset);
if (complete_round && block == last_seen_block &&
offset >= last_offset) {
break;
}
if (offset >= block->length) {
offset = 0;
block = QTAILQ_NEXT(block, next);
if (!block) {
block = QTAILQ_FIRST(&ram_list.blocks);
complete_round = true;
}
} else {
uint8_t *p;
int cont = (block == last_sent_block) ?
RAM_SAVE_FLAG_CONTINUE : 0;
@ -467,16 +483,7 @@ static int ram_save_block(QEMUFile *f, bool last_stage)
break;
}
}
offset += TARGET_PAGE_SIZE;
if (offset >= block->length) {
offset = 0;
block = QTAILQ_NEXT(block, next);
if (!block)
block = QTAILQ_FIRST(&ram_list.blocks);
}
} while (block != last_seen_block || offset != last_offset);
}
last_seen_block = block;
last_offset = offset;