[Qemu-devel] Re: Extremely slow graphic updates

[lsorense@csclub.uwaterloo.ca (Lennart Sorensen)]

On Tue, Jan 20, 2009 at 03:21:59PM +0000, Stefano Stabellini wrote:
> There are no such cases I am aware of.

Hopefully not.  So far I looked at 'is_buffer_shared' and so far it
always returns 0, so at least that seems to indicate it isn't using
shared memory (I believe).

> Are you using Xorg in the guest? What is the guest color depth?

No.  Just text console.  Of course the text console is a framebuffer
being that it is emulating a powermac g3.  I don't pass any arguments to
qemu-system-ppc other than -hda and a disk image.  So whatever the
default is.
 
> I assume your host is an i386 machine.
> What is the color depth of your Xorg server running on the host?

Well I run 24bit on my machine, and then use ssh -X to reach the machine
I run qemu on, so it would be 24bit (probably 32bit really).  The
machine running qemu is running i386 (although the kernel is amd64, not
that it matters).

Here is a diff of dmesg from the vnc boot to the default X mode (slow):

# diff -u /tmp/dmesg.normal.vnc.log /tmp/dmesg.slow.log
--- /tmp/dmesg.normal.vnc.log   2009-01-20 10:46:56.000000000 -0500
+++ /tmp/dmesg.slow.log 2009-01-20 10:45:17.000000000 -0500
@@ -39,17 +39,17 @@
 GMT Delta read from XPRAM: 0 minutes, DST: off
 WARNING: Estimating decrementer frequency (not found)
 WARNING: Estimating processor frequency (not found)
-time_init: decrementer frequency = 16.604350 MHz
+time_init: decrementer frequency = 38.257166 MHz
 time_init: processor frequency   = 1000.000000 MHz
-clocksource: timebase mult[f0e6962] shift[22] registered
-clockevent: decrementer mult[440] shift[16] cpu[0]
+clocksource: timebase mult[688e3a3] shift[22] registered
+clockevent: decrementer mult[9cb] shift[16] cpu[0]
 Console: colour dummy device 80x25
 console handover: boot [udbg0] -> real [tty0]
 Dentry cache hash table entries: 32768 (order: 5, 131072 bytes)
 Inode-cache hash table entries: 16384 (order: 4, 65536 bytes)
 High memory: 0k
 Memory: 138692k/147456k available (3760k kernel code, 8600k reserved, 152k data, 347k bss, 220k init)
-Calibrating delay loop... 33.15 BogoMIPS (lpj=66304)
+Calibrating delay loop... 76.28 BogoMIPS (lpj=152576)
 Security Framework initialized
 SELinux:  Disabled at boot.
 Capability LSM initialized
@@ -76,7 +76,7 @@
 Freeing initrd memory: 2383k freed
 Thermal assist unit using timers, shrink_timer: 500 jiffies
 audit: initializing netlink socket (disabled)
-type=2000 audit(1232466137.128:1): initialized
+type=2000 audit(1232465912.752:1): initialized
 VFS: Disk quotas dquot_6.5.1
 Dquot-cache hash table entries: 1024 (order 0, 4096 bytes)
 msgmni has been set to 275
@@ -111,7 +111,7 @@
 TCP cubic registered
 NET: Registered protocol family 17
 registered taskstats version 1
-platform ppc-rtc.0: setting system clock to 2009-01-20 15:42:17 UTC (1232466137)
+platform ppc-rtc.0: setting system clock to 2009-01-20 15:38:35 UTC (1232465915)
 Freeing unused kernel memory: 220k init
 ADB mouse at 3, handler set to 2
 input: ADB mouse as /class/input/input2

The decrementer frequency is very difference, as are the bogomips and the timebase.

I was trying to come up with a simple test case to show the problem,
but found another one.  If I simply run qemu-system-ppc -vnc :1 I get
nothing on VNC.  Using -sdl I get the openbios prompt.  If I use both
-vnc :1 and -sdl I get openbios showing on both.  vnc by itself seems to
only start displaying something once something other than openbios is
running, like the bootloader or linux kernel.  That doesn't seem right.

Test case:

Get the debian lenny (testing) business card iso from (60MB)
http://cdimage.debian.org/cdimage/daily-builds/daily/arch-latest/powerpc/iso-cd/debian-testing-powerpc-businesscard.iso

qemu-system-ppc -cdrom debian-testing-powerpc-businesscard.iso

at openbios prompt type 'boot cdrom:'

hit enter to accept default choices at yaboot prompt and debian location
prompts.  Stop when it gets to asking which mirror to use.  Switch to
the second VT using alt+F2.

run 'sleep 5'.  Time how long it really takes.  Mine takes about 13 or
14 seconds.

Previous to 6336 it took 5 seconds.  When using VNC, it takes 5 seconds,
although since you don't see the openbios prompt in vnc mode, it's
tricky to do this.  I did my test after doing an install so that it
boots.

-- 
Len Sorensen