Re: [Xen-devel] Re: [PATCH 0 of 12] PV on HVM Xen

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 18 May 2010, Christian Tramnitz wrote:
> Hi Stefano,
> 
> what are the particular advantages of running PVonHVM vs. traditional PV 
> (vs pure HVM)?
> I'd like to update the wiki with some info about it...
> 

Sorry for the late reply, but I wanted to have some numbers to compare
the three cases...

PVonHVM guests are as easy to install, use and maintain as pure HVM
guests but provide performances comparable or even better than
traditional PV guests.

In particular you'll find that PVonHVM guests are always faster than
pure HVM guests, most of the times faster than 64 bit PV guests but
probably slower than 32 bit PV guests.


The following are the results of kernbench run in optimal mode on a 4
vcpu linux guest with 512MB of ram.
The host is a Dell Precision T3500 (HAP enabled):
testbox:~# cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 26
model name      : Intel(R) Xeon(R) CPU           E5520  @ 2.27GHz
stepping        : 5
cpu MHz         : 2266.806
cache size      : 8192 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 11
wp              : yes
flags           : fpu de tsc msr pae mce cx8 apic sep mtrr mca cmov pat clflush 
acpi mmx fxsr sse sse2 ss ht nx constant_tsc pni est ssse3 sse4_1 sse4_2 popcnt 
ida
bogomips        : 4538.00
clflush size    : 64
power management:

processor       : 1
vendor_id       : GenuineIntel
cpu family      : 6
model           : 26
model name      : Intel(R) Xeon(R) CPU           E5520  @ 2.27GHz
stepping        : 5
cpu MHz         : 2266.806
cache size      : 8192 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 11
wp              : yes
flags           : fpu de tsc msr pae mce cx8 apic sep mtrr mca cmov pat clflush 
acpi mmx fxsr sse sse2 ss ht nx constant_tsc pni est ssse3 sse4_1 sse4_2 popcnt 
ida
bogomips        : 4538.00
clflush size    : 64
power management:

processor       : 2
vendor_id       : GenuineIntel
cpu family      : 6
model           : 26
model name      : Intel(R) Xeon(R) CPU           E5520  @ 2.27GHz
stepping        : 5
cpu MHz         : 2266.806
cache size      : 8192 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 11
wp              : yes
flags           : fpu de tsc msr pae mce cx8 apic sep mtrr mca cmov pat clflush 
acpi mmx fxsr sse sse2 ss ht nx constant_tsc pni est ssse3 sse4_1 sse4_2 popcnt 
ida
bogomips        : 4538.00
clflush size    : 64
power management:

processor       : 3
vendor_id       : GenuineIntel
cpu family      : 6
model           : 26
model name      : Intel(R) Xeon(R) CPU           E5520  @ 2.27GHz
stepping        : 5
cpu MHz         : 2266.806
cache size      : 8192 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 11
wp              : yes
flags           : fpu de tsc msr pae mce cx8 apic sep mtrr mca cmov pat clflush 
acpi mmx fxsr sse sse2 ss ht nx constant_tsc pni est ssse3 sse4_1 sse4_2 popcnt 
ida
bogomips        : 4538.00
clflush size    : 64
power management:



64 bit PV on HVM
----------------
Average Optimal load -j 4 Run (std deviation):
Elapsed Time 215.307 (10.1294)
User Time 632.503 (6.4785)
System Time 115.497 (4.53905)
Percent CPU 347.333 (15.885)
Context Switches 43319.7 (2088.39)
Sleeps 48950 (3140.18)

64 bit pure HVM
---------------
Average Optimal load -j 4 Run (std deviation):
Elapsed Time 235.25 (4.10598)
User Time 512.48 (1.69714)
System Time 73.5967 (0.65041)
Percent CPU 248.667 (4.93288)
Context Switches 35930.3 (342.837)
Sleeps 56249.7 (2784.42)

64 bit traditional PV
---------------------
Average Optimal load -j 4 Run (std deviation):
Elapsed Time 248.187 (12.3954)
User Time 535.283 (0.818189)
System Time 127.497 (0.342685)
Percent CPU 266.667 (12.8582)
Context Switches 32978 (2968.78)
Sleeps 54391.3 (3141.44)


the results show that the 64 bit PV on HVM case is the fastest but it is
also the one that uses most CPU and User time.

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