* Vincent Palatin (vpala...@chromium.org) wrote:
> 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.
Nice catch.
> 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.
Hopefully this is back on par with before the QLIST switchover.
> Signed-off-by: Vincent Palatin <vpala...@chromium.org>
Acked-by: Chris Wright <chr...@redhat.com>
> ---
> 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);
> + }
Pretty close to self-documenting code now. Not sure if it's subtle enough
to warrant change to the comment like:
/* Move block to head of list if it's not there already */
thanks,
-chris
