[Xen-users] CPU Usage statistics Issue

[Richard Warburton <richard.warburton@xxxxxxxxx>]

Hey,

I'm currently trying to measure the CPU Usage of a process that's
running on a Linode VM, which is virtualised using Xen.  It appears to
exhibit very weird CPU Usage statistics and I was wondering if anyone
could explain how/why this is happening.   I am running a series of
processes, each of which entirely pegs a core.

Pegging 1 Core = 14% of CPU
Pegging 2 Cores = 28% of CPU
Pegging 3 Cores = 60% of CPU
Pegging 4 Cores = 100% of CPU

Those are the CPU stats as listed in both vmstat and top - so I'm
presuming that they're coming from /proc/stat.  I'm not seeing any
'steal' time at all, so I presume that I have access to all the CPU
cores nominally available, I have appended the contents of
/proc/cpuinfo to the bottom of the page.  The weird thing is that if
you look at the processes' individual CPU Usage measurement then it is
listed as 100% (ie a whole core).  I would consequently expected
vmstat to be listing 25%, 50%, 75%, 100% on a 4 core box.  Thanks for
any help explaining what is going on here.

regards,

  Richard

processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 26
model name      : Intel(R) Xeon(R) CPU           L5520  @ 2.27GHz
stepping        : 5
cpu MHz         : 2266.746
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 cx8 cmov pat clflush mmx fxsr sse
sse2 ss ht nx constant_tsc nonstop_tsc pni ssse3 sse4_1 sse4_2 popcnt
hypervisor
bogomips        : 4533.49
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management:

processor       : 1
vendor_id       : GenuineIntel
cpu family      : 6
model           : 26
model name      : Intel(R) Xeon(R) CPU           L5520  @ 2.27GHz
stepping        : 5
cpu MHz         : 2266.746
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 cx8 cmov pat clflush mmx fxsr sse
sse2 ss ht nx constant_tsc nonstop_tsc pni ssse3 sse4_1 sse4_2 popcnt
hypervisor
bogomips        : 4533.49
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management:

processor       : 2
vendor_id       : GenuineIntel
cpu family      : 6
model           : 26
model name      : Intel(R) Xeon(R) CPU           L5520  @ 2.27GHz
stepping        : 5
cpu MHz         : 2266.746
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 cx8 cmov pat clflush mmx fxsr sse
sse2 ss ht nx constant_tsc nonstop_tsc pni ssse3 sse4_1 sse4_2 popcnt
hypervisor
bogomips        : 4533.49
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management:

processor       : 3
vendor_id       : GenuineIntel
cpu family      : 6
model           : 26
model name      : Intel(R) Xeon(R) CPU           L5520  @ 2.27GHz
stepping        : 5
cpu MHz         : 2266.746
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 cx8 cmov pat clflush mmx fxsr sse
sse2 ss ht nx constant_tsc nonstop_tsc pni ssse3 sse4_1 sse4_2 popcnt
hypervisor
bogomips        : 4533.49
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management:

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