Le 18/01/2012 11:48, Alon Levy a écrit :
On Wed, Jan 18, 2012 at 11:39:13AM +0100, Dominique Rodrigues wrote:
Le 18/01/2012 11:32, Alon Levy a écrit :
On Wed, Jan 18, 2012 at 11:27:14AM +0100, Dominique Rodrigues wrote:
Le 18/01/2012 11:18, Alon Levy a écrit :
On Wed, Jan 18, 2012 at 09:54:49AM +0100, Dominique Rodrigues wrote:
Le 18/01/2012 09:44, Alon Levy a écrit :
On Wed, Jan 18, 2012 at 08:06:40AM +0100, Dominique Rodrigues wrote:
Hi,

Since I use qxl driver in virtual desktop powered by qemu-kvm, I
found a strange problem with Gimp.

After launching Gimp, open a new windows, and then try to draw
something. It appears that the drawing is very slow and does not
follow the mouse at all.

It is the same if I use spicy, spicec or vnc to connect to my
virtual desktop.

This problem does not appear with cirrus or vmware graphic drivers.

I found that on any Linux distribution (CentOS, RHEL, Scientific
Linux, Debian, Ubuntu).

I currently use :
- qemu-kvm 1.0 compiled with spice support
- spice-protocol 0.10.1
- spice 0.10
- spice-gtk 0.7
- xorg-qxl driver 0.16

Is there any explanation for that ?
I would assume it is qxl driver cpu bound on something, probably busy
waiting on the command ring. Can you run perf top on the guest?

Indeed, during the drawing in Gimp, Xorg takes between 55% and 66% of CPU.

After, Xorg goes down to 0.3%.

(Test done on CentOS 6.2 guest, with 1280 Mb vRAM)
ok, can you drill down - you should be able to install the debug symbols
for the qxl driver (xorg-x11-drv-qxl package) and see the specific
functions that are taking the most time.

I installed qxl driver from freedesktop.org :

# wget -c 
http://xorg.freedesktop.org/releases/individual/driver/xf86-video-qxl-0.0.16.tar.bz2
# tar xvfj xf86-video-qxl-0.0.16.tar.bz2
# cd xf86-video-qxl-0.0.16
# ./configure --libdir=/usr/lib64 --prefix=/usr CFLAGS='-O3'
# make
# make install

Do you mean that I should use CFLAGS with "-g" ?
I think that's it, yes.

Ok. So how do you profile debug messages afterwhile ?

If I "tail -f /var/log/Xorg.0.log", the only message I got is :

  Bad bpp: 1 (1)

Other messages look standard.

Right, that's not interesting. What I meant was:

# yum install perf
# perf top
copy paste the top entries.

Ok, that's it (from a screenshot of the VM):

samples    pcnt    function        DSO

3796.00 60.4% hashlittle /usr/lib64/xorg/modules/drivers/qxl_drv.so
2014.00        32.1%    __memcpy_ssse3      /lib64/libc-2.12.so
341.00 5.4% download_box /usr/lib64/xorg/modules/drivers/qxl_drv.so
61.00               1.0%    __memset_sse2        /lib64/libc-2.12.so
11.00 0.2% qxl_ring_push /usr/lib64/xorg/modules/drivers/qxl_drv.so
10.00               0.2%    finish_task_switch    [kernel.kallsyms]
8.00 0.1% qxl_allocnf /usr/lib64/xorg/modules/drivers/qxl_drv.so
8.00                 0.1%    retint_careful            [kernel.kallsyms]
6.00 0.1% hash_and_copy /usr/lib64/xorg/modules/drivers/qxl_drv.so

Regards,

--


        Dominique Rodrigues

nanoClouD<http://www.nanocloud.com>
8, rue Lemercier
75017 Paris
France
standard : +33 1 77 69 64 38
529 002 743 R.C.S. Paris
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