Re: x86_64 emulation on ppc64le POWER9 hardware - no multi threading

[Kim-Norman Sahm]

Hi Cedric,

could you send me your complete xml file?
I get the error: process exited while connecting to monitor: 
2020-08-03T17:43:50.146851Z qemu-system-x86_64: The -accel and "-machine 
accel=" options are incompatible.

Best regards
KIm

Am 03.08.20, 19:37 schrieb "Cédric Le Goater" <clg@kaod.org>:

    Again, with a correct answer,

    On 8/3/20 3:47 PM, Kim-Norman Sahm wrote:
    > hi,
    > 
    >  
    > 
    > i’m running Debian 10 on POWER9 and would like to spawn x86_64 emulated 
VMs.
    > 
    > The virtual machine is configured to run with 8 vpus but it’s very slow.
    > 
    > On the host you can see that the qemu-system-x86_64 process is using just 
one core!
    > 
    >  
    > 
    > Ppc64le guests are using multi cores, so its looks like an config problem 
or software bug with the x86 emulator.

    On a Power9 host (20.04), I did the following changes to an x86 domain :

      <domain type='qemu' 
xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>

    and at the end of the domain file  :
      <qemu:commandline>
        <qemu:arg value='-accel'/>
        <qemu:arg value='tcg,thread=multi'/>
      </qemu:commandline>

    The topology is defined as : 

      <cpu mode='custom' match='exact' check='none'>
        <model fallback='forbid'>qemu64</model>
        <topology sockets='1' cores='12' threads='2'/>
      </cpu>

    The VM is using MTTCG, as reported by top on the host :

        PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ 
COMMAND
    5761 libvirt+  20   0   23.5g   1.8g  21888 R  2167   1.4   6:10.82 
qemu-system-x86

    In the guest :

    $ lscpu 
    Architecture:                    x86_64
    CPU op-mode(s):                  32-bit, 64-bit
    Byte Order:                      Little Endian
    Address sizes:                   40 bits physical, 48 bits virtual
    CPU(s):                          24
    On-line CPU(s) list:             0-23
    Thread(s) per core:              1
    Core(s) per socket:              24
    Socket(s):                       1
    NUMA node(s):                    1
    Vendor ID:                       AuthenticAMD
    CPU family:                      6
    Model:                           6
    Model name:                      QEMU Virtual CPU version 2.1.0
    Stepping:                        3
    CPU MHz:                         511.035
    BogoMIPS:                        1022.07
    Virtualization:                  AMD-V
    L1d cache:                       1.5 MiB
    L1i cache:                       1.5 MiB
    L2 cache:                        12 MiB
    NUMA node0 CPU(s):               0-23
    Vulnerability L1tf:              Not affected
    Vulnerability Mds:               Not affected
    Vulnerability Meltdown:          Not affected
    Vulnerability Spec store bypass: Vulnerable
    Vulnerability Spectre v1:        Mitigation; usercopy/swapgs barriers and 
__user
                                      pointer sanitization
    Vulnerability Spectre v2:        Mitigation; Full generic retpoline, STIBP 
disab
                                     led, RSB filling
    Flags:                           fpu de pse tsc msr pae mce cx8 apic sep 
mtrr pg
                                     e mca cmov pat pse36 clflush mmx fxsr sse 
sse2 
                                     ht syscall nx lm nopl cpuid pni cx16 
popcnt hyp
                                     ervisor lahf_lm cmp_legacy svm abm sse4a 
3dnowp
                                     refetch vmmcall


    Cheers,

    C.