Re: [Xen-devel] Problem Xen 4.0-amd64 + Heartbeat 3.0.3-2 with Debian Squeeze

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Sat, 2011-05-28 at 22:21 +0100, gilmarlinux@xxxxxxxxxxxxxxx wrote:
> I thought it might be something I / O xen causing this in heartbeat.

"I / O"? I'm not sure what this means.

I wonder if this is just simply down to scheduling latencies? i.e. dom0
simply isn't getting scheduled frequently enough to meet the
requirements of the heartbeat process.

I assume this doesn't happen when there is no domU workload to contend
with dom0? What sort of workloads are your guests running? How many
VCPUs do you have in total?

As an experiment you could try playing with the scheduling priorities
for dom0, e.g. giving it more weight.

Another experiment you could try is pinning a dom0 VCPU to a PCPU,
pinning the heartbeat process to that VCPU and excluding domU VCPUs from
contention by pinning them to the remaining PCPUs.

IIRC these sorts of latency sensitive workloads are somewhere that the
existing credit scheduler doesn't do so well and is something which
George is looking to address with credit2. His canonical workload of
this type is audio playback but I suppose heartbeat falls into the same
broad class. So it might also be worth trying the credit2 scheduler.

You could also try Xen 4.1, IIRC some band-aids were applied to the
credit1 scheduler between 4.0 and 4.1.

Lastly you could presumably configure heartbeat to be less sensitive to
these latencies? I also hope that the heartbeat process sets itself up
with the Linux scheduler to be a fairly high priority process within
dom0?

Ian.



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