vnc_update_client currently scans the dirty bitmap of each client
bitwise which is a very costly operation if only few bits are dirty.
vnc_refresh_server_surface does almost the same.
this patch optimizes both by utilizing the heavily optimized
function find_next_bit to find the offset of the next dirty
bit in the dirty bitmaps.
The following artifical test (just the bitmap operation part) running
vnc_update_client 65536 times on a 2560x2048 surface illustrates the
performance difference:
All bits clean - vnc_update_client_new: 0.07 secs
vnc_update_client_old: 10.98 secs
All bits dirty - vnc_update_client_new: 11.26 secs
vnc_update_client_old: 20.19 secs
Few bits dirty - vnc_update_client_new: 0.08 secs
vnc_update_client_old: 10.98 secs
The case for all bits dirty is still rather slow, this
is due to the implementation of find_and_clear_dirty_height.
This will be addresses in a separate patch.
Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
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