From patchwork Thu Mar 10 20:47:46 2011 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: Fix performance regression in qemu_get_ram_ptr Date: Thu, 10 Mar 2011 10:47:46 -0000 From: Vincent Palatin X-Patchwork-Id: 86335 Message-Id: <1299790066-768-1-git-send-email-vpalatin@chromium.org> To: Qemu devel Cc: Chris Wright , Alex Williamson , Vincent Palatin , Anthony Liguori 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 Acked-by: Alex Williamson Acked-by: Chris Wright --- exec.c | 7 +++++-- 1 files changed, 5 insertions(+), 2 deletions(-) diff --git a/exec.c b/exec.c index d611100..81f08b7 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); } }