Re: [PATCH v1 1/4] xen: add real time scheduler rt

[Meng Xu <xumengpanda@gmail.com>]

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Hi Jan,


2014-08-29 5:05 GMT-04:00 Jan Beulich <JBeulich@suse.com>:

> >>> On 28.08.14 at 18:06, <xumengpanda@gmail.com> wrote:
> > ​As to your concern "I still don't see why such wouldn't be
> > applicable uniformly to all schedulers."​, are you suggesting that the
> > credit and credit2 scheduler could also allow users to set/get each
> VCPU's
> > parameters? (I think that could be possible but this should be some
> design
> > decision made by credit and credit2 scheduler developer?)
>
> Perhaps. But I think a more uniform interface to the individual
> schedulers would help on the tools side too. But in the end I'm
> just raising questions/concerns here, it's George who needs to
> be okay with your approach.
>

​Thank you very much for your questions and suggestions!

BTW, the ARINC653 scheduler in Xen also specifies each VCPU's parameters.
It's just FYI. :-)

In xen/include/public/sysctl.h, it specifies each vcpu's parameter in
sched_entries array.

/*

 * This structure is used to pass a new ARINC653 schedule from a

 * privileged domain (ie dom0) to Xen.

 */

struct xen_sysctl_arinc653_schedule {

    /* major_frame holds the time for the new schedule's major frame

     * in nanoseconds. */

    uint64_aligned_t     major_frame;

    /* num_sched_entries holds how many of the entries in the

     * sched_entries[] array are valid. */

    uint8_t     num_sched_entries;

    /* The sched_entries array holds the actual schedule entries. */

    struct {

        /* dom_handle must match a domain's UUID */

        xen_domain_handle_t dom_handle;

        /* If a domain has multiple VCPUs, vcpu_id specifies which one

         * this schedule entry applies to. It should be set to 0 if

         * there is only one VCPU for the domain. */

        unsigned int vcpu_id;

        /* runtime specifies the amount of time that should be allocated

         * to this VCPU per major frame. It is specified in nanoseconds */

        uint64_aligned_t runtime;

    } sched_entries[ARINC653_MAX_DOMAINS_PER_SCHEDULE];

};


>
> >> I think anything going into the seconds, not to speak of minutes or
> >> hours, range is already beyond boundaries of being reasonable /
> >> useful.
> >
> > ​Hmm, that's fair. If we want to limit the range to seconds, then uint32
> is
> > enough. However, what if some user really want to set the period/budget
> to
> > hours/days? Then we couldn't support it if we use uint32 type for
> > period/budget. (This is just my subtle concern. I'm not arguing that we
> > have to use uint64 or uint32. As long as everyone agrees with a type, I
> can
> > just change it to the agreed type very quickly.) Do you have any
> suggestion
> > of how we can reach an agreement and get the range finalized? ​
>
> Let's see what others, mainly George and Dario, think.
>

​Sure! Thanks!

Meng​


-- 


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

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