Re: Interrupt time inflation on Xen

[Johnny Billquist <bqt%softjar.se@localhost>]

On 2016-03-14 00:08, Thor Lancelot Simon wrote:
> I had occasion a couple of days ago to try to block-copy a very large
> filesystem from a xen dom0 to another machine across a fast local network.
>
> I tried this:
>
> sysctl -w kern.sbmax=10000000
> sysctl -w net.inet.tcp.sendbuf_auto=0
> dd if=/dev/rsd0g bs=1048576 | ttcp -t -b 2097152 -l 131072 -fm -p 9001 172.0.0.1
>
> On the far end, I had simply the corresponding ttcp -r job (with corresponding
> socket/tcp sysctls in place) redirected to a file.
>
> The underlying hardware is a RAID5 of 300GB SAS drives on an Areca 1680.
> The Ethernet controller in use is a 'wm'.  All supported offload functionality
> is turned on (turning it off just slows things down).
>
> Shockingly, I saw the system go to 0% idle time, with 45-55% "Interrupt"
> and the rest "System".  Interrupts per second were a comparatively low 1500,
> about 500 disk and 1000 network.  Throughput was horrible -- about 35MB/sec.

This might not be related, or useful, but it do sound similar to what 
I've been seeing on VAXen for a few years now. I get unexpectedly high 
interrupt rates, but most significantly, I can get ridiculous system 
time when doing something like a "cvs update". I have never had the time 
to try and figure it out, but I normally have over 50% (usually around 
70%) in system when doing this. Which does not seem reasonable.

But once more, this might be a red herring, so feel free to ignore.

	Johnny