From 7d82af38b78305155553013c6fd709dc50404199 Mon Sep 17 00:00:00 2001 From: Vincent Palatin Date: Thu, 10 Mar 2011 15:47:46 -0500 Subject: [PATCH] Fix performance regression in qemu_get_ram_ptr 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 Signed-off-by: Anthony Liguori --- exec.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/exec.c b/exec.c index d611100dc..81f08b784 100644 --- a/exec.c +++ b/exec.c @@ -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); } }