Red Hat Bugzilla – Bug 841330
Regression in performance of kernel 3.4.4 vs. 3.3.7 when running as Xen Dom0
Last modified: 2013-02-13 20:29:29 EST
Description of problem:
I run Xen with Fedora 16 serving as Dom0. I have found that upgrading to kernel 3.4.4 degrades the performance of both Dom0 (i.e., itself) and DomU (i.e., other kernels) vs. 3.3.7.
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. Boot 3.4.4 as Dom0.
2. Build glibc-2.16.0 with "time make".
3. Boot 3.3.7 and repeat.
3.4.4 and 3.3.7 should have similar performance.
Looking at /proc/cpuinfo, I noticed that 3.3.7 provides flag aperfmperf and 3.4.4 provides hw_pstate (but not vice versa).
Created attachment 598953 [details]
/proc/cpuinfo while running kernel 3.4.4
Adding Konrad on CC.
I booted Xen using the Linux 3.4.4 kernel while passing "cpufreq=verbose,performance" to Xen. I confirmed that Xen booted using this argument by checking the output of "xl dmesg". I saw slow results similar to those on 3.4.4 above:
One more thing, just to eliminate this being the power management fault. Can you on the Linux command line boot with 'xen-acpi-processor.off=1'?
Did you this performance regression start with 3.4.0? Did you try to see if removing some of the commits that I posted on xen-devel had any effect?
That does it. Setting 'xen-acpi-processor.off=1' restores the performance I see on 3.3.7.
I have not yet been able to back any of the commits from my kernel.
(In reply to comment #5)
> That does it. Setting 'xen-acpi-processor.off=1' restores the performance I
> see on 3.3.7.
Yeey! So the cpufreq=performance on the Xen hypervisor line _should_ have done it too. Hmm.
When you ran with 'cpufreq=performance,verbose' did you get any extra Xen output? I am quite curious to see what kind of powersave information it had uploaded that either caused the hypervisor to slow down or .. it its a bug in the hypervisor.
Check with 'xl dmesg' please.
I am leaning towards the latter, so what kind of machine is this? What's the motherboard/RAM? Is the hypervisor a custom compiled one or did you just use the default Fedora one?
> I have not yet been able to back any of the commits from my kernel.
That is Ok. The xen-acpi-processor.off=1 is the failsafe I added in case something would go wrong (which it seems it has).
Also, could I ask you to email Xen-devel on the email thread with these findings (and the motheroad/CPU) so that we can CC the AMD folks to see if they know what is up with the hypervisor.
Created attachment 600871 [details]
Output from "xl dmesg" with cpufreq=verbose,performance, but NOT xen-acpi-processor.off=1
Motherboard: ASUS M5A97, BIOS version 0901
Processor: AMD FX 4170 quad core, 4.2GHz, 12.0MB total cache
Memory: 16GB DDR3 1,151MHz
The hypervisior is standard Fedora xen-4.1.2-8.fc16.x86_64.
xen-4.1.2-10.fc16 has been submitted as an update for Fedora 16.
I have built xen-4.1.2-10.fc16 which includes the patch
which it has been suggested might fix this problem.
xen-4.1.3-1.fc16 has been submitted as an update for Fedora 16.
* should fix your issue,
* was pushed to the Fedora 16 testing repository,
* should be available at your local mirror within two days.
Update it with:
# su -c 'yum update --enablerepo=updates-testing xen-4.1.3-1.fc16'
as soon as you are able to.
Please go to the following url:
then log in and leave karma (feedback).
without any special boot parameters. The glibc build completed as follows:
So this combination still has a performance regression (vs. 3.3.7 in the initial comment).
Actually, I was too quick on my last comment. I followed the instructions from the Fedora Update System too closely and forgot to update xen-hypervisor, etc (i.e., I only updated the xen package).
Here are my new results:
This is still a bit slower but much less so, and it may be due to the imprecision of my "benchmark".
xen-4.1.3-1.fc16 has been pushed to the Fedora 16 stable repository. If problems still persist, please make note of it in this bug report.
Something again is wrong.
I am using the same machine with:
When I boot in Xen, I notice a performance degredation. When I boot with "xen-acpi-processor.off=1" all is well.
Created attachment 640247 [details]
Output from "xl dmesg" with cpufreq=verbose,performance, but NOT xen-acpi-processor.off=1; kernel and Xen from latest comment
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