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On 23/05/13 15:17, Fabio Fantoni wrote:
Il 23/05/2013 12:54, George Dunlap ha
scritto:
On
23/05/13 11:39, Andrew Cooper wrote:
On 23/05/13 11:36, Fabio Fantoni wrote:
Il 23/05/2013 09:39, Jan Beulich ha
scritto:
On 22.05.13 at 18:54, George
Dunlap <george.dunlap@xxxxxxxxxxxxx>
wrote:
On 22/05/13 17:30, Pasi KÃrkkÃinen wrote:
On Wed, May 22, 2013 at
04:05:27PM +0100, George Dunlap wrote:
Hmm, for testing, can we use cpuid to mask out SSE,
and then try qxl ?
That had occurred to me -- Andrew / Jan, do you know
which flag might
disable this particular instruction?
I guess we could try just disabling all the SSE
instructions.
movdqu is an SSE2 instruction, so disabling bit 26 of
CPUID EDX
output to EAX=1 input.
Can you explain better please?
Should I add this to test it?
cpuid="host,sse=0,sse2=0,ssse3=0,sse4_1=0,sse4_2=0,eax=1"
It will likely not work. SSE2 is an architectural requirement
for 64bit.
It means that 64bit code may assume the presence of SSE2. Xen
amongst
other software does make this assumption.
It might work if he's using 32-bit.
Fabio, as I said in my initial e-mail, you need to:
1. Run "cat /proc/cpuinfo" on your dom0
2. Look at the line that says "features:"
3. Find all the things that contain "sse" > 2 (sse2, ssse3,
&c)
4. Set them to 0 in the "cpuid" field like above.
Every processor will be a bit different -- you can't just copy
mine and expect it to work.
Don't include "eax=1" -- Jan is thinking of a different
interface.
Â-George
Tried with Raring (ubuntu 13.04) 32bit...
in cfg:
cpuid="host,sse=0,sse2=0,ssse3=0,sse4_1=0,sse4_2=0"
# xl create /etc/xen/RARING.cfg
Parsing config from /etc/xen/RARING.cfg
while parsing CPUID flag: "sse4_1=0":
 error #2: unknown CPUID flag name
while parsing CPUID flag: "sse4_2=0":
 error #2: unknown CPUID flag name
Right -- in that case this is a minor bug in libxl. (Actually I got
the same result, I just didn't notice the error messages -- sorry
about that.)
In domU:
# cat /proc/cpuinfo | grep sse
flagsÂÂÂÂÂÂÂÂÂÂ : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr
pge mca cmov
Âpat pse36 clflush mmx fxsr ht nx rdtscp lm constant_tsc pni cx16
sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer hypervisor
lahf_lm
What should I do to have sse4 disabled?
For now with sse, sse2 and sse3 disabled the performance is very
very low (even without qxl), while performances are acceptables
with SSE.
I got the same results with qxl card and qxl driver loaded, but
now at least X and qemu didn't crash.
Sorry, same result as what? Does the X driver work or not?
According to the results it seems that the only blocking task for
qxl is full sse support. I think also that full sse support can
improve general domU perfomances.
Just to be clear, normally SSE is provded by the processor; the vast
majority of the time SSE instructions will work just fine. The
particular problem here is that instructions talking to qemu need to
be emulated by Xen. Xen will emulate SSE2 instructions, but not if
the amount of data transferred is over 8 bytes.
Getting that particular instruction to work is definitely going to
be a work item for 4.4; but it's too late in the release process to
do anything for 4.3 at this point.
Â-George
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