Re: [Qemu-devel] [dpdk-dev] Will huge page have negative effect on guest vm in qemu enviroment?

[Chris Friesen <chris.friesen@windriver.com>]

On 06/21/2017 01:16 PM, Dr. David Alan Gilbert wrote:
> * Sam (batmanustc@gmail.com) wrote:
>> Thank you~
>>
>> 1. We have a compare test on qemu-kvm enviroment with huge page and without
>> huge page. Qemu start process is much longer in huge page enviromwnt. And I
>> write an email titled with '[DPDK-memory] how qemu waste such long time
>> under dpdk huge page envriment?'. I could resend it later.
>
>> 2. Then I have another test on qemu-kvm enviroment with huge page and
>> without huge page, which I didn't start ovs-dpdk and vhostuser port in qemu
>> start process. And I found Qemu start process is also much longer in huge
>> page enviroment.
>>
>> So I think huge page enviroment, which grub2.cfg file is specified in
>> ‘[DPDK-memory]
>> how qemu waste such long time under dpdk huge page envriment?’, will really
>> have negative effect on qemu start up process.
>>
>> That's why we don't like to use ovs-dpdk. Althrough ovs-dpdk is faster, but
>> the start up process of qemu is much longer then normal ovs, and the reason
>> is nothing with ovs but huge page. For customers, vm start up time is
>> important then network speed.
>
> How are you setting up hugepages?  What values are you putting in the
> various /proc or cmdline options and how are you specifying them on
> QEMU's commandline.
>
> I think one problem is that with hugepages qemu normally allocates them
> all at the start;  I think there are cases where that means moving a lot
> of memory about, especially if you lock it to particular NUMA nodes.


For what it's worth, we use something like this:

-object 
memory-backend-file,id=ram-node0,prealloc=yes,mem-path=/mnt/huge-2048kB/libvirt/qemu,share=yes,size=2147483648,host-nodes=0,policy=bind 
-numa node,nodeid=0,cpus=0-3,memdev=ram-node0

and I haven't noticed it taking particularly long to start up.  All our 
hugepages are reserved at host startup though.

Chris