* 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