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Fix performance regression in qemu_get_ram_ptr

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When the commit f471a17e9d869df3c6573f7ec02c4725676d6f3a converted the
ram_blocks structure to QLIST, it also removed the conditional check before
switching the current block at the beginning of the list.

In the common use case where ram_blocks has a few blocks with only one
frequently accessed (the main RAM), this has a performance impact as it
performs the useless list operations on each call (which are on a really
hot path).

On my machine emulation (ARM on amd64), this patch reduces the
percentage of CPU time spent in qemu_get_ram_ptr from 6.3% to 2.1% in the
profiling of a full boot.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Vincent Palatin 2011-03-10 15:47:46 -05:00 committed by Anthony Liguori
parent d48751ed4f
commit 7d82af38b7
1 changed files with 5 additions and 2 deletions
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7
exec.c
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@ -2957,8 +2957,11 @@ void *qemu_get_ram_ptr(ram_addr_t addr)
QLIST_FOREACH(block, &ram_list.blocks, next) {
if (addr - block->offset < block->length) {
QLIST_REMOVE(block, next);
QLIST_INSERT_HEAD(&ram_list.blocks, block, next);
/* Move this entry to to start of the list. */
if (block != QLIST_FIRST(&ram_list.blocks)) {
QLIST_REMOVE(block, next);
QLIST_INSERT_HEAD(&ram_list.blocks, block, next);
}
return block->host + (addr - block->offset);
}
}