Re: Extreme console latency during disk IO (8.0-RC1, previous releases also affected according to others)

On Tue, 13 Oct 2009, Ivan Voras wrote:

Robert N. M. Watson wrote:

On 13 Oct 2009, at 14:33, Ivan Voras wrote:

If (1) is highly variable during I/O, it's almost certainly a property of
the VM technology you're using, and there's nought to be done about it in
the guest OS.

Here's an example of a ping session with 0.1s resolution during a few
seconds-stall in ssh:

64 bytes from 161.53.72.188: icmp_seq=1576 ttl=64 time=0.383 ms
64 bytes from 161.53.72.188: icmp_seq=1577 ttl=64 time=0.405 ms
64 bytes from 161.53.72.188: icmp_seq=1578 ttl=64 time=0.360 ms

64 bytes from 161.53.72.188: icmp_seq=2304 ttl=64 time=4.194 ms
64 bytes from 161.53.72.188: icmp_seq=2305 ttl=64 time=0.454 ms
64 bytes from 161.53.72.188: icmp_seq=2306 ttl=64 time=0.376 ms

note huge packet loss. It looks like it's VM fault or something like it.

It sounds like the VM is failing to execute the guest during certain types of I/O. A bit of scheduler tracing in the host OS probably wouldn't go amiss to confirm that the VM really is suspending the guest

It's VMWare ESXi underneath, which is *Officially Not Linux* though some ducks may disagree - anyway, I suspect tracing the host in this way is next to impossible without some kind of diamondium-level contract.

What information do you need? I have a platinum VMWare contract.

What version of ESXi?

LER

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--
Larry Rosenman http://www.lerctr.org/~ler
Phone: +1 512-248-2683 E-Mail: ler@xxxxxxxxxx
US Mail: 430 Valona Loop, Round Rock, TX 78681-3893
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