Re: [Xen-devel] Notes on stubdoms and latency on ARM

[Volodymyr Babchuk <vlad.babchuk@xxxxxxxxx>]

Hi Stefano,

On 19 June 2017 at 10:54, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote:

>> But given the conversation so far, it seems likely that that is mainly
>> due to the fact that context switching on ARM has not been optimized.
>
> True. However, Volodymyr took the time to demonstrate the performance of
> EL0 apps vs. stubdoms with a PoC, which is much more than most Xen
> contributors do. Nodoby provided numbers for a faster ARM context switch
> yet. I don't know on whom should fall the burden of proving that a
> lighter context switch can match the EL0 app numbers. I am not sure it
> would be fair to ask Volodymyr to do it.
Thanks. Actually, we discussed this topic internally today. Main
concern today is not a SMCs and OP-TEE (I will be happy to do this
right in XEN), but vcopros and GPU virtualization. Because of legal
issues, we can't put this in XEN. And because of vcpu framework nature
we will need multiple calls to vgpu driver per one vcpu context
switch.
I'm going to create worst case scenario, where multiple vcpu are
active and there are no free pcpu, to see how credit or credit2
scheduler will call my stubdom.
Also, I'm very interested in Julien's idea about stubdom without GIC.
Probably, I'll try to hack something like that to see how it will
affect overall switching latency.

-- 
WBR Volodymyr Babchuk aka lorc [+380976646013]
mailto: vlad.babchuk@xxxxxxxxx

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