Re: KVM got slow after adding more physical memory to host - SOLVED

Nikola Ciprich
2011-09-06T19:22:44Z

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Hello guys,

thanks to both of You for Your replies. The problem is solved,
exactly as Avi said, the DMA in windows got somehow disabled.
So this certainly was not related to adding the memory...

anyways, note for further generations:
in windows XP, the DMA usage can be checked in
Device Manager->IDE ATA/ATAPI Controllers -> Properties->Advanced Settings
Current Transfer Mode must be Multi-Word DMA2 or something similar,
NOT PIO!

The way I enabled this, was to uninstall both primary and secondary controller
in device controller, then also uninstall Intel controller, and THEN rebooting (NOT sooner!)
after reboot, controllers got detected and installed again, with DMA properly enabled.
Note that when controller is in PIO mode, this is really a patience test, switching to DMA took
me like half an hour to complete, so slow the system was :-/

So thanks a lot for Your help once more.

have a nice day.

nik

On Tue, Sep 06, 2011 at 08:01:47PM +0300, Avi Kivity wrote:
> On 09/06/2011 07:30 PM, Nikola Ciprich wrote:
>> OK, seems like Avi's right, at least the windows guest is not using DMA
>> though the question is, why did it got disabled
>
> It can happen due to a timeout, perhaps a temporary load spike.
>
>> and how can I reenable it,
>
> Google knows.
>
>> I'm not experienced that much with XP :(
>>
>>
>> > It is rep/in-out. But why it became noticeable only after adding more
>> > physical memory to the host is a mystery.
>>
>> now that I'm thinking about it, we had similar problem in the past, the windows guest
>> was unusably slow, and the whole host was slow as well... upgrading to 0.14.1 seemingly
>> solved this issue, but maybe the DMA just got randomly enabled, and now after adding
>> the memory (and restarting of course), it just got disabled again?
>> but why could this be??
>>
>
> I don't think it's related to the memory.
>
> --
> error compiling committee.c: too many arguments to function
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