Ian,
I had screwed up and had a process running in dom0 chewing up CPU in
dom0. I thought I had taken care of it.
After fixing that, most of the numbers for dom0, domU, and the base SLES
kernel are within a couple of tenths of percent of each other. However,
there are some fairly large differences in some of the runs where the
socket buffers are small.
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec
262142 262142 4096 60.00 941.03 base
262142 262142 4096 60.00 939.95 dom0
262142 262142 4096 60.00 937.22 domU
16384 16384 32768 60.00 379.68 base
16384 16384 32768 60.00 350.15 dom0
16384 16384 32768 60.00 367.89 domU
In the latter case, the divergence from the base performance is much
larger. I assume that when the socket buffers are small, the extra
overhead for the interrupts is showing up more because more interrupts
are required.
Overall, though, the numbers are now acceptable. Thanks for your help.
It allowed me to spot my goof. (Sorry about wasting your time though.)
One last question: is there an easy way to break out the amount of CPU
time spent in the hypervisor?
Thanks,
John Byrne
Ian Pratt wrote:
Both dom0 and the domU are SLES 10, so I don't know why the "idle"
performance of the two should be different. The obvious asymmetry is
the
disk. Since the disk isn't direct, any disk I/O by the domU would
certainly impact dom0, but I don't think there should be much, if any.
I
did run a dom0 test with the domU started, but idle and there was no
real change to dom0's numbers.
What's the best way to gather information about what is going on with
the domains without perturbing them? (Or, at least, perturbing
everyone
equally.)
As to the test, I am running netperf 2.4.1 on an outside machine to
the
dom0 and the domU. (So the doms are running the netserver portion.) I
was originally running it in the doms to the outside machine, but when
the bad numbers showed up I moved it to the outside machine because I
wondered if the bad numbers were due to something happening to the
system time in domU. The numbers is the "outside" test to domU look
worse.
It might be worth checking that there's no interrupt sharing happening.
While running the test against the domU, see how much CPU dom0 burns in
the same period using 'xm vcpu-list'.
To keep things simple, have dom0 and domU as uniprocessor guests.
Ian
Ian Pratt wrote:
There have been a couple of network receive throughput
performance regressions to domUs over time that were
subsequently fixed. I think one may have crept in to 3.0.3.
The report was (I believe) with a NIC directly assigned to the domU,
so
not using netfront/back at all.
John: please can you give more details on your config.
Ian
Are you seeing any dropped packets on the vif associated with
your domU in your dom0? If so, propagating changeset
11861 from unstable may help:
changeset: 11861:637eace6d5c6
user: kfraser@xxxxxxxxxxxxxxxxxxxxx
date: Mon Oct 23 11:20:37 2006 +0100
summary: [NET] back: Fix packet queuing so that packets
are drained if the
In the past, we also had receive throughput issues to domUs
that were due to socket buffer size logic but those were
fixed a while ago.
Can you send netstat -i output from dom0?
Emmanuel.
On Mon, Nov 06, 2006 at 09:55:17PM -0800, John Byrne wrote:
I was asked to test direct I/O to a PV domU. Since, I had a system
with two NICs, I gave one to a domU and one dom0. (Each is
running the
same
kernel: xen 3.0.3 x86_64.)
I'm running netperf from an outside system to the domU and
dom0 and I
am seeing 30% less throughput for the domU vs dom0.
Is this to be expected? If so, why? If not, does anyone
have a guess
as to what I might be doing wrong or what the issue might be?
Thanks,
John Byrne
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