Re: [Xen-devel] [PATCH RFC v1 4/4] libxc for rt scheduler

[Meng Xu <xumengpanda@xxxxxxxxx>]

Hi Dario,

Â

> My concern is: Will the former one has worse performance than the
> later one? Ââ
>

Well, Xen has its tricks, but yes, I think performing e.g., 8 or 16
hypercalls in a loop is worse than issueing one returning an array.

It also must be noted that, getting and setting scheduling parameters,
should not happen in very critical path, so it probably won't matter
much.

Anyway, as said above, go for the array first if you like it better.
When you do that, consider Andrew's comments to the bottom of patch 1:

"As a gut feel, I think that these two ints should be part of the struct
xen_domctl_sched_rt below, with a guest handle pointing to an array of {
period, budget } structures, which avoids the LEGACY_MAX limit."

I don't think you'll need vcpu_index any longer, and I'm not sure
whether you need max_vcpus to be part of the interface of this hcall, or
if you're better out fetching it from some other call, though.

âYes, I don't need the max_vcpus any more after I improve this interface. I think I will use the array for the get operation, since as Andrew mentioned that batching is better than doing hypercall one by one when it involves more than one hypercalls. As to the set operation, I think I can avoid using array. Anyway, I will do this first and let people decide if we need to make further change. :-)Â

(BTW, I will modify the code base on your other comments in the previous email.)

Thanks,

Meng

--

-----------
Meng Xu
PhD Student in Computer and Information Science
University of Pennsylvania

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