Created attachment 415074 [details]
script for pipe test

Description of problem:


Version-Release number of selected component (if applicable):
qemu-kvm-0.12.1.2-2.54.el6.x86_64

How reproducible:
100%

Steps to Reproduce:
1. boot guest with x2apic (at least 2 vcpus, and enable ept in host)
2. command
/usr/libexec/qemu-kvm  -smp 2 -m 2G -drive file=/root/images/rhel6-32.qcow2,if=virtio,boot=on -net nic,vlan=0,macaddr=00:90:4a:01:00:37,model=virtio -net tap,vlan=0,script=/etc/qemu-ifup  -uuid `uuidgen` -no-hpet -usbdevice tablet  -rtc-td-hack  -startdate now -cpu qemu64,+x2apic -monitor stdio -vnc :1
3. run pipetest (attached), and get the result
4. boot guest without x2apic (same vcpu num as step1)
5. run pipetest, and get the result
6. compare the results.

Another testing:
run lmbench testing, and compare "Pipe latency"

  
Actual results:
pipetest:

with x2apic
56.19 usecs/loop.
56.45 usecs/loop.
57.05 usecs/loop.
56.48 usecs/loop.
55.45 usecs/loop.
55.13 usecs/loop.
53.89 usecs/loop.
54.55 usecs/loop.
55.93 usecs/loop.
57.98 usecs/loop.
56.59 usecs/loop.
54.89 usecs/loop.
54.25 usecs/loop.
54.25 usecs/loop.
56.51 usecs/loop.

without x2apic:
56.46 usecs/loop.
57.22 usecs/loop.
54.03 usecs/loop.
56.65 usecs/loop.
56.33 usecs/loop.
54.25 usecs/loop.
54.51 usecs/loop.
56.18 usecs/loop.
56.07 usecs/loop.
54.83 usecs/loop.
55.41 usecs/loop.
56.31 usecs/loop.
56.48 usecs/loop.
56.30 usecs/loop.
56.12 usecs/loop.
56.16 usecs/loop.


lmbench testing:

with x2apic:
Pipe latency: 72.7915 microseconds

without x2apic:
Pipe latency: 71.0693 microseconds 


Expected results:


Additional info:

1. host:
tree : RHEL6.0-20100511.3/  

processor	: 7
vendor_id	: GenuineIntel
cpu family	: 6
model		: 26
model name	: Intel(R) Core(TM) i7 CPU         920  @ 2.67GHz
stepping	: 4

flags		: fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts rep_good xtopology nonstop_tsc aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm sse4_1 sse4_2 popcnt lahf_lm ida tpr_shadow vnmi flexpriority ept vpid


2. guest: rhel6-32