Re: [Xen-devel] [PATCH v6 for Xen 4.7 1/4] xen: enable per-VCPU parameter settings for RTDS scheduler

[Meng Xu <mengxu@xxxxxxxxxxxxx>]

On Tue, Mar 15, 2016 at 1:22 PM, Chong Li <lichong659@xxxxxxxxx> wrote:
> On Tue, Mar 15, 2016 at 11:41 AM, Dario Faggioli
> <dario.faggioli@xxxxxxxxxx> wrote:
>> On Tue, 2016-03-15 at 11:22 -0500, Chong Li wrote:
>>> On Mon, Mar 14, 2016 at 5:05 AM, Dario Faggioli
>>> <dario.faggioli@xxxxxxxxxx> wrote:
>>> >
>>
>> We said 'once' and then 'once per domain', but something I'd be fine
>> with (coupled with keeping G_WARNING) would be 'once per operation'.
>> Basically, if a domain has 128 vcpus, and an hypercall tries to set all
>> of them to period=100, budget=50, we just print the warning once. Then,
>> if after a while the sysadmin tries the same again, we again just log
>> once, etc.
>>
>> Doing this seems much easier, as the 'warned' flag could just be a
>> local variable of the hypercall implementation. I'm quite sure that
>> would work if there is not any continuation/re-issueing mechanism in
>> the hypercall in question. BUT in our case there is, so things may be
>> more complicated... :-/
>>
>> Had you thought about a solution like this already? If no, can you see
>> whether there is a nice and easy way to make something like what I just
>> described above to work in our case?
>>
> How about:
>
> We create a global variable in sched_rt.c:
>     /* This variable holds its value through hyerpcall re-issueing.
>      * When finding vcpu settings with too low budget or period (e.g,
> 100 us), we print a warning
>      * and set this variable "true". No more warnings are printed
> until this variable
>      * becomes false.
>      */
>     static bool warned;
> Initialize it as "false" in rt_init().
> In your example,
> we "warned = true" when we find the first vcpu has budget less than
> 100 us. Outside
> of the while loop, we do:
>     if ( index == op->u.v.nr_vcpus ) /* no more hypercall re-issueing */
>         warned = false;
>
Hi Chong,

I don't think creating a global variable just for the warning thing is
a better idea. Even if we do want such a variable, it should only
occur in rt_dom_cntl() function, since it is only used in
rt_dom_cntl().
Global variable should be used "globally", isn't it. ;-)

Thanks,

Meng
-----------
Meng Xu
PhD Student in Computer and Information Science
University of Pennsylvania
http://www.cis.upenn.edu/~mengxu/

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