Richard,
Not sure if you've tried this, but I noticed massive performance gains
(easily booting 2-3 times as fast) by converting from RAW disk images to
direct-mapped raw partitions and making sure that IOMMU support was
enabled in the BIOS and in the kernel at boot time. The obvious downside
to using raw partitions is a loss of flexibility and portability across
physical machines, but in some cases the trade-offs may be worth it.
I never ran any formal benchmarks, but it "felt" like about a 50%
performance boost going from RAW disk images to raw partitions (don't
even think about using QCOW2 disk images for Windows, your VM's will
still be booting next week...). The real gains, which I can't yet fully
explain, came from passing "iommu=on intel_iommu=on" to the host kernel
on bootup. I believe the boot option to enable IOMMU support may be
different on AMD hardware.
Granted, this is on a much smaller VM than you're using (Windows 7 x64
with two vCPUs and 4gb of vRAM), but might be worth investigating.
Good luck!
-- Robert Vineyard
On 08/17/2012 08:36 AM, Richard Davies wrote:
Hi Avi,
Thanks to you and several others for offering help. We will work with Avi at
first, but are grateful for all the other offers of help. We have a number
of other qemu-related projects which we'd be interested in getting done, and
will get in touch with these names (and anyone else who comes forward) to
see if any are of interest to you.
This slow boot problem is intermittent and varys in how slow the boots are,
but I managed to trigger it this morning with medium slow booting (5-10
minutes) and link to the requested traces below.
The host in question has 128GB RAM and dual AMD Opteron 6128 (16 cores
total). It is running kernel 3.5.1 and qemu-kvm 1.1.1.
In this morning's test, we have 3 guests, all booting Windows with 40GB RAM
and 8 cores each (we have seen small VMs go slow as I originally said, but
it is easier to trigger with big VMs):
pid 15665: qemu-kvm -nodefaults -m 40960 -smp 8 -cpu host,hv_relaxed \
-vga cirrus -usbdevice tablet -vnc :99 -monitor stdio -hda test1.raw
pid 15676: qemu-kvm -nodefaults -m 40960 -smp 8 -cpu host,hv_relaxed \
-vga cirrus -usbdevice tablet -vnc :98 -monitor stdio -hda test2.raw
pid 15653: qemu-kvm -nodefaults -m 40960 -smp 8 -cpu host,hv_relaxed \
-vga cirrus -usbdevice tablet -vnc :97 -monitor stdio -hda test3.raw
We are running with hv_relaxed since this was suggested in the previous
thread, but we see intermittent slow boots with and without this flag.
All 3 VMs are booting slowly for most of the attached capture, which I
started after confirming the slow boots and stopped as soon as the first of
them (15665) had booted. In terms of visible symptoms, the VMs are showing
the Windows boot progress bar, which is moving very slowly. In top, the VMs
are at 400% CPU and their resident state size (RES) memory is slowly
counting up until it reaches the full VM size, at which point they finish
booting.
Here are the trace files:
http://users.org.uk/slow-win-boot-1/ps.txt (ps auxwwwf as root)
http://users.org.uk/slow-win-boot-1/top.txt (top with 2 VMs still slow)
http://users.org.uk/slow-win-boot-1/trace-console.txt (running trace-cmd)
http://users.org.uk/slow-win-boot-1/trace.dat (the 1.7G trace data file)
http://users.org.uk/slow-win-boot-1/trace-report.txt (the 4G trace report)
Please let me know if there is anything else which I can provide?
Thank you,
Richard.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
