RE: [Xen-devel] Xen as a kernel module

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> Secondly, there have been repeated reports on this list of 
> people having 
> problems with lower performance in domU than in dom0, perhaps due to 
> cheap hardware, perhaps just due to misconfiguration, 

I think most of these problems were down to debugging accidently getting
enabled in the stable build. We seem to be back to normal performance
now.

I think there are still some issues with particular ioapic's, but this
code is about to get rewritten and moved into dom0 anyhow. 

> and the 
> figures on 
> the Xen website have not been updated to reflect what the actual 
> situation is, so I guess nobody knows what the overhead will 
> look like 
> for a specific type of application. 

The performance figures for SPECCPU, OSDB/PostgreSQl, SPECWeb99/Apache,
Postmark etc are pretty much identical between 2.0 and 1.2 --- see the
"Safe Hardware Access with the Xen Virtual Machine Monitor" paper. The
new IO model tends to burn more CPU for a given IO rate, but under high
load things pipeline reasonably nicely and the privilege transitions are
amortized. Latency does suffer, but it was never that great under 1.2
anyhow. Smarter NICs will help this a lot (e.g. see the Arsenic paper by
myself and Keir).

Ian


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