Re: [Qemu-devel] [PATCH 2/4] vnc: allow the Buffer to shrink again

[Peter Lieven]

Am 03.09.2015 um 11:52 schrieb Gerd Hoffmann:
> On Do, 2015-08-27 at 11:39 +0100, Daniel P. Berrange wrote:
> > On Thu, Aug 27, 2015 at 12:18:52PM +0200, Peter Lieven wrote:
> > > currently the Buffer can only grow. This increases Qemu memory footprint
> > > dramatically since normally the biggest VNC updates are at connection time.
> > > But also after a VNC session has terminated there is one persistent buffer
> > > in queue->buffer which I have seen to increase to over 100MB and it is never
> > > getting smaller again.
> > Do you have any idea what caused the buffer to increase to 100MB in size
> > in the first place ? I would expect a full screen update would cause the
> > biggest buffer usage, and even for a 1920x1140 screen that should not
> > be anywhere near 100MB in size. IOW, i'm wondering if the 100MB usage
> > is symptomatic of a more serious bug somewhere else in the VNC code
> > that you're just masking you reducing buffer size afterwards.
> Cooked up a buffer stats patch (attached).
> Buffer sizes are nowhere near 100MB for me (as expected by Daniel).
> Individual buffers are in the 1 -> 4 MB range (1920x1080), even summed
> up this is more like 10 not 100 MB.
>
> So, big question remains why they are that big for you?

Simple case to create at least a reasonable allocation: -vga vmware and a 
client that prefers Hextile encoding.

~/git/qemu$ x86_64-softmmu/qemu-system-x86_64 -m 4096 -enable-kvm -cdrom  
~/Downloads/ubuntu-14.04.3-desktop-amd64.iso -k de -usb -device usb-tablet 
-nodefaults -serial null -parallel null -cpu Westmere,enforce -vga vmware 
-monitor stdio -vnc :0
QEMU 2.4.50 monitor - type 'help' for more information
(qemu) buffer_reserve: 11/out    :    4 kB
buffer_reserve: 11/in     :    4 kB
buffer_reserve: queue     :    4 kB
buffer_reserve: queue     :    8 kB
buffer_reserve: 11/jobs   :    8 kB
buffer_reserve: 11/out    :   16 kB
buffer_reserve: queue     :   16 kB
buffer_reserve: queue     :   32 kB
buffer_reserve: queue     :   64 kB
buffer_reserve: queue     :  128 kB
buffer_reserve: queue     :  256 kB
buffer_reserve: 11/jobs   :  256 kB
buffer_reserve: 11/out    :  256 kB
buffer_reserve: queue     :  512 kB
buffer_reserve: queue     : 1024 kB
buffer_reserve: queue     : 2048 kB
buffer_reserve: 11/jobs   : 2048 kB
buffer_reserve: 11/out    : 2048 kB
buffer_reserve: queue     : 4096 kB
buffer_reserve: queue     : 8192 kB
buffer_reserve: queue     : 16384 kB
buffer_reserve: 11/jobs   : 16384 kB
buffer_reserve: 11/out    : 16384 kB

Its not 100MB, but 50MB.

Same with Tight encoding:

(qemu) buffer_reserve: 11/out    :    4 kB
buffer_reserve: 11/in     :    4 kB
buffer_reserve: queue     :    4 kB
buffer_reserve: 11/t-tight:    4 kB
buffer_reserve: 11/t-tight:    8 kB
buffer_reserve: 11/t-tight:   16 kB
buffer_reserve: 11/t-tight:   32 kB
buffer_reserve: 11/t-tight:   64 kB
buffer_reserve: 11/t-tight:  128 kB
buffer_reserve: 11/t-tight:  256 kB
buffer_reserve: 11/t-tight:  512 kB
buffer_reserve: 11/t-zlib :    4 kB
buffer_reserve: 11/jobs   :    4 kB
buffer_reserve: 11/t-zlib :   64 kB
buffer_reserve: 11/t-tight: 1024 kB
buffer_reserve: 11/t-tight: 2048 kB
buffer_reserve: 11/t-tight: 4096 kB
buffer_reserve: 11/t-tight: 8192 kB
buffer_reserve: 11/t-tight: 16384 kB
buffer_reserve: 11/t-zlib :  128 kB
buffer_reserve: queue     :    8 kB
buffer_reserve: 11/jobs   :    8 kB
buffer_reserve: 11/out    :    8 kB
buffer_reserve: 11/t-zlib :  256 kB
buffer_reserve: queue     :   64 kB
buffer_reserve: queue     :  128 kB
buffer_reserve: queue     :  256 kB
buffer_reserve: queue     :  512 kB
buffer_reserve: queue     : 1024 kB
buffer_reserve: queue     : 2048 kB
buffer_reserve: queue     : 4096 kB
buffer_reserve: queue     : 8192 kB
buffer_reserve: 11/jobs   : 8192 kB
buffer_reserve: 11/out    : 8192 kB

~40MB.

Peter