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xen-devel
[Xen-devel] [PATCH - proposed] XI Shadow Page Table Mechanism
A post last week contained the design document for a shadow page
table mechanism. This post contains more information, and a pointer
to the code.
As a recap, the "XI Shadow Mechanism" is a design for shadow
page table code for fully virtualized HVM domains running on a 64-bit
Xen hypervisor.
This work was undertaken to address a number of goals. These are
enumerated in the document posted last week and include:
- ability to run fully virtualized 32, 32PAE and 64 bit guest
domains concurrently on a 64-bit hypervisor
- start support of live migration of fully virtualized domains
- provide good performance and robustness
- limit size and scope of change to Xen hypervisor
This design has been coded, and tested on a variety of operating
systems. I've included this weekend's test report.
Of particular interest from the following table are the Average Time
comparisions (smaller is better):
pfault 10.56 vs 2.43 (XI)
sync_all 39.72 vs 33.51 (XI)
invl_pg 22.75 vs 4.00 (XI)
The patch is too large for the mailing list, and may be obtained from
http://s3.amazonaws.com/VIDownloads/xi-20060626.patch
The patch applies against changeset 10352 (and possibly others)
We look forward to any comments and suggestions.
Thanks,
-b
XI Shadow Test Report
This report shows a comparsion of test runs done on xen-unstable changeset
10352 with and without the XI patch applied. It also compares pfault,
sync_all, and invl_pg performance.
With the XI patch 32bit SMP (PAE) guests now boot and pass the regression
tests, closing Bug #661. With the XI patch 64bit SMP guests are much more
stable and are no longer experiencing SEGVs and GPFs, closing Bug #678.
----------------------------------------------------------------------
| XEN | Guest Kernel SMP kernels booted with 2 CPUs |
| Changeset|-----------------------------------------------------------|
| | 32bit Non-XI | 32bit XI | 64bit Non-XI | 64bit XI |
| |--------------|--------------|--------------|--------------|
| | Boot | Test | Boot | Test | Boot | Test | Boot | Test |
|----------|------|-------|------|-------|------|-------|------|-------|
| 10352 | Fail | | Pass | 852/1 | Pass | 852/0 | Pass | 852/0 |
| | (1) | | | (2) | |(3,4,5)| |(3,4) |
----------------------------------------------------------------------
1. BUG 661: 32bit SMP guest crashes on boot:
"(XEN) __hvm_bug at vmx.c:2289"
2. BUG 666: 32bit UP guest fail ltp gettimeofday02:
"Time is going backwards"
3. BUG 663: 64bit SMP guest report these messages while running:
"(XEN) spurious IRQ irq got=-1"
4. BUG 662: 64bit SMP guest report this message in ltp pth_str01/2/3:
"(XEN) <vlapic_accept_irq>level trig mode repeatedly for vector 252"
5. BUG 678: 64bit 2CPU SMP guest failed several ltp tests with SEGVs or GPF
"sshd[23654] general protection rip:2a9555d426 rsp:7fbfffd000 error 0"
The XI patch can be enabled or disabled at build time and includes some
performance statistics that can be examined whether or not it's enabled.
This allows us to compare the performance of XI vs the existing shadow code.
You access the statistics from the XEN console (^a^a^a). Typing a 'Y'
clears the counters and a 'y' displays the counters since the last clear.
Here is a comparsion of XI vs Non-XI shadow code done on xen-unstable
changeset 10352. The guest is a RHEL4U2-64bit 2 CPU SMP 256MB Guest running
a usex -b24 load for 5 minutes. Shadow statistics cleared at start of run.
(XEN) Non-XI shadow performance statistics for the last 303 seconds
(XEN) Op type # of Operations
Total Avg Tick Profile
(XEN) <2usec <3usec <4usec <8usec <16usec <32usec
<64usec >=64usec ops/msec usec In Op Locked Total
(XEN) pfault 6750685 1128922 624988 3249437 3833201 2863229
1224908 315992 19991362 10.56 0 0 0
(XEN) 33.7% 5.6% 3.1% 16.2% 19.1% 14.3%
6.1% 1.5% 211175
(XEN) sync_all 8176 380 333 159011 167619 305470
814598 298411 1753998 39.72 0 0 0
(XEN) 0.4% 0.0% 0.0% 9.0% 9.5% 17.4%
46.4% 17.0% 69670
(XEN) invl_pg 219 17 114 23333 40087 21904
24622 4639 114935 22.75 0 0 0
(XEN) 0.1% 0.0% 0.0% 20.3% 34.8% 19.0%
21.4% 4.0% 2615
(XEN) XI shadow performance statistics for the last 302 seconds
(XEN) Op type # of Operations
Total Avg Tick Profile
(XEN) <2usec <3usec <4usec <8usec <16usec <32usec
<64usec >=64usec ops/msec usec In Op Locked Total
(XEN) pfault 23078414 4694139 485499 613419 396088 1427265
11976 8228 30715028 2.43 0 0 0
(XEN) 75.1% 15.2% 1.5% 1.9% 1.2% 4.6%
0.0% 0.0% 74690
(XEN) sync_all 1734 97 169 305433 484991 174300
150199 130405 1247328 33.51 0 0 0
(XEN) 0.1% 0.0% 0.0% 24.4% 38.8% 13.9%
12.0% 10.4% 41810
(XEN) invl_pg 10169 302977 125270 44927 5385 17603
776 1656 508763 4.00 0 0 0
(XEN) 1.9% 59.5% 24.6% 8.8% 1.0% 3.4%
0.1% 0.3% 2037
--
------------------------------------------------------------------------
Ben Thomas Virtual Iron Software
bthomas@xxxxxxxxxxxxxxx Tower 1, Floor 2
978-849-1214 900 Chelmsford Street
Lowell, MA 01851
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