The patch checks if the guest continuously writes 3
times to the same guest page table pages, if yes, then unshadow the guest pages.
The idea is copied from the KVM side. And since the idea has overlapped with
the now optimization in the now Xen shadow code, so the patch removes the
optimization part which when the guest writes 2 continuously 0 to the same page,
then unshadow the guest page.
In the latest Xen, if we use iperf to test the NIC
assigned to HVM guest, we will find that the performance data is very unstable
and low especially with an ia32pae guest. The root cause is that Xen holds the
guest page table pages even when they changes to data pages, and at that time
if guest write pure data to the paged, Xen will get many unnecessary pages
faults. It hurts the iperf performance a lot. The patch resolves the issue
(compare to the old optimization). And considering the side effects to the
other benchmark, we have a test result as followed.
|
Benchmark
|
Guest OS
|
with out the patch
|
with the patch
|
Gain(+)/Downgrade(-)
|
|
|
|
|
|
|
|
Sysbench
|
Windows XP (32pae)
|
58.4704
|
58.8196
|
-0.59%
|
|
|
Windows XP (ia32e)
|
31.2266
|
31.6322
|
-1.30%
|
|
Specjbb
|
Linux (32pae)
|
1530.52
|
1525.27
|
-0.34%
|
|
|
Linux (ia32e
|
975.94
|
970.44
|
-0.56%
|
|
Kernel Build
|
Linux (32pae)
|
1m44s
|
1m43s
|
+0.96%
|
|
|
Linux (ia32e)
|
2m38s
|
2m23s
|
+9.5%
|
|
Sysmark2007
|
|
|
|
|
|
E-learning
|
Windows XP (32pae)
|
55
|
56
|
+1.8%
|
|
Video Creation
|
Windows XP (32pae)
|
49
|
48
|
-2%
|
|
Productivity (cannot run)
|
|
|
|
|
|
3D (cannot run)
|
|
|
|
|
|
Iperf
|
Linux (32pae)
|
Very unstable from ~50M/bs to 500M/bs
|
Stable ~550M/bs
|
|
Signed-off-by
Xin Xiaohui xiaohui.xin@xxxxxxxxx
Signed-off-by
Dong Eddie <eddie.dong@xxxxxxxxx>
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