[Xapian-discuss] Search performance issues and profiling/debugging

[Alexandre Gauthier]

Chris Good a écrit :
> Ron Kass wrote:
>   
>> Not sure what you mean by "other VMs could well be confusing your results"
>> We use XenServer on this machine, but we have only one instance (DomU), 
>> and only this instance is running everything locally. So there are no 
>> other VMs to confuse things, and even if there were, they have nothing 
>> to do with the VM we run the test on or with the test itself.
>> (Can you clarify what you mean?)
>>     
>
> If you have multiple VMs sharing the same hardware then activity on one
> will obviously affect the performance on other VMs.  Since you're running
> a lone DomU other DomUs aren't going to be competing for resources but 
> it's possible that something in Dom0 is getting swapped in and running.
>
> How are you accessing your drives, is DomU accessing the raw devices or is
> it mapped via virtual files from Dom0?
>
> Is it possible to run these tests either directly from Dom0 or even better
> with a non-xen kernel?
>
> Given your current configuration of a single VM xen isn't adding anything 
> so removing it would eliminate any side-effects of it.  I also suspect
> that it would cure your oprofile issue.
>
> Chris
>
>   
Sorry to intrude, but if I may offer some insight, the Dom0 instance in 
a Xen set-up is just as paravirtualized as a DomU -- it just has control 
access to memory inside DomUs, and offers the drivers back-end 
interfaces. The Dom0 and DomUs both run on top of the Xen kernel.

Also, if he is running a commercial Xen from XenSource, he won't have 
access to the Dom0, which is a custom frankenstein mix of SuSE and RHEL 
witth no other puprose but to control the DomUs, a bit like ESX.

The question of the DomU's disk mapping is still valid, and I'd be 
curious to hear the answer. I also think Xen is responsible for the 
oprofile troubles, I get that on a Debian DomU as well.

I hope this vaguely helps...

Alex