Re: [Qemu-devel] [PATCHv2 3/6] ui/vnc: optimize dirty bitmap tracking

[Eric Blake]

On 11/21/2013 01:51 AM, Peter Lieven wrote:
> 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

s/artifical/artificial/

> 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.

s/addresses/addressed/

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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