On 20/08/2011 15:13, Ben Hutchings wrote:
On Sat, 2011-08-20 at 12:44 +0100, Richard Kettlewell wrote:
The emulated screen was blank and
did not respond to any input. The kernel log is full of messages as
shown below. They almost all name the same executable, apache_accesses
(from package munin-node) and have the same backtraces, but are
different PIDs (it is not a long-running process).
The exception is a "BUG: soft lockup - CPU#0 stuck for 35s!" message,
also below.
The guest is a news server, with around a kilobyte/second of network
traffic going into it at all times.
The guest has 512MB RAM assigned. It has a gigabyte of swap available
and doesn't seem to have been using much of it.
[...]
That does sound wrong.
Could it be that the host is slow to service the guest's disk I/O?
In summary, it does seem to be.
Average latency on /dev/vda over the last week is reported as around
200ms. There are occasional spikes to multiple whole seconds.
A couple of those spikes are approximately the right time for 'BUG: soft
lockup' messages (but the resolution is not very high) & there are other
spikes with no corresponding messages in the kernel logs.
That said there are similar huge latency spikes visible for the host
too. I think I need some faster storage l-(
As for throughput, a quick test with dd reveals the guest has about 10%
of the write performance of the host, which seems pretty poor to me.
ttfn/rjk
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