Re: [Xen-users] 99% iowait on one core in 8 core processor

[Matthias <matthias.kannenberg@xxxxxxxxxxxxxx>]

Hi Ian,

sorry, but it's still not working..

I rebooted the server, then manually started irqbalanced just to be
sure, then started xen and the domUs.. still the same as above: every
I/O related is done by cpu0 (even after hours of running 5 domUs). i
see some spikes on the other cpu's, but i think this is due to domUs
using their assigned vcpus and xentop shows a distribution of cputime,
too..

I started irqbalance in debug modus once and it complained that my
hardware is not numa compatible. Might this be an issue? From what I
read, xen should support proper scheduling on non-numa hardware and
only the numa-support is new and might be a bit quirky..

checked my smp_affinity stuff then: currently, it shows the following for a domU
smp_affinity: 01
smp_affinity_list: 0

tried to change smp_affinity to 3f (=111111 for my 6vcpu) and it was
changed immediately back to 01.. thought that was irqbalance going
rogue but after stopd the deamon, this still happens..

so my take is: something is setting the irq to only use cpu0 and
changes i do manually or which are done by irqbalance are overwritten
constantly making irqbalance useless..

Any idea what this can be? supposently something within xen?



2012/7/12 Ian Campbell <ian.campbell@xxxxxxxxxx>:
> On Thu, 2012-07-12 at 13:04 -0400, Matthias wrote:
>>
>> Any other idea how we can make xen utilize the other (v)cpus for it's
>> I/O stuff?
>
> Are you sure irqbalanced is running? Some versions had a bug and would
> crash on a Xen system (they crash if there is no irq 0 or something like
> that). Even if it is running it can take some time for irqbalanced to
> realise that things are unbalanced and start moving stuff around.
>
> There are ways in Linux to manually balance IRQs. You have to much
> around with /proc/irq/*/smp_affinity*
>
> Really irqbalanced should be doing this for you though.
>
> Ian.
>
>

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