Re: [Qemu-discuss] VM tuning

[Peter Kieser]

1. Make sure that the cache is disabled in the guest (cache=none)
2. Look at the Redhat profiles ('tuned') for virtual-host which 
specifies the following sysctl knobs:

kernel.sched_min_granularity_ns=10000000
kernel.sched_wakeup_granularity_ns=15000000
vm.dirty_ratio=10
vm.dirty_background_ratio=5
vm.swappiness=10

Having a higher dirty_ratio will cause larger amounts of I/O to be 
cached in memory - but it will also cause the I/O to hit the disk all at 
once and have un-even I/O patterns which could be causing the issues you 
are seeing.

-Peter


On 2013-10-04 9:07 AM, Stephan von Krawczynski wrote:
> Hi Peter,
>
> I know the deadline stuff, this is already in. But the problem arises
> nevertheless. My idea is that mv.dirty_ratio should be a lot higher to prevent
> the lagging, probably around 80.

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