Re: [Xen-devel] How to Stop scheduler

[Pankaj Parakh <me.pankajparakh@xxxxxxxxx>]

How to disable softirq in Xen, if I want that no function should be
able to raise SCHEDULE_SOFTIRQ, how can I do that??

On Thu, Nov 5, 2009 at 3:25 PM, George Dunlap
<George.Dunlap@xxxxxxxxxxxxx> wrote:
> I assume you mean, once you've paused current(), how do you get into
> the scheduler to actually get it off the cpu?
>
> In Linux, you can call schedule() because each process has its own
> kernel stack allocated to it; the stack "remembers" where each process
> was in the kernel, so you can return from schedule() at the same place
> in the kernel once you're scheduled again.
>
> Xen only has one stack per cpu, so it cannot keep track of where *in
> the hypervisor* a vcpu is that gets scheduled out.  Therefore, you
> can't call schedule() directly, as it would throw away the stack.  You
> must raise SCHEDULE_SOFTIRQ on the current cpu, and then return back
> to the guest.  On the way out, the softirq will call schedule() and
> switch to another vcpu if necessary.  (It will only schedule the idle
> process if there are no runnable vcpus.)
>
> grep for SCHEDULE_SOFTIRQ to see examples of how this is used in Xen.
>
>  -George
>
> On Thu, Nov 5, 2009 at 12:43 AM, Pankaj Parakh
> <me.pankajparakh@xxxxxxxxx> wrote:
>> How can I schedule idle vcpu voluntarily without using schedule() ??
>> Is there any function for it already defined, or do I have to follow
>> some steps.. ??
>>
>> On Wed, Nov 4, 2009 at 5:09 PM, George Dunlap
>> <George.Dunlap@xxxxxxxxxxxxx> wrote:
>>>
>>> On Wed, Nov 4, 2009 at 5:59 AM, Pankaj Parakh <me.pankajparakh@xxxxxxxxx> 
>>> wrote:
>>> > If I take domain_update_lock for  a domain, what will happen to its
>>> > interrupts for IO completions or any other type..??
>>> > And will it be scheduled if I hold that lock..??
>>>
>>> Have you looked at the interrupt delivery / IO completion path, or the
>>> scheduler path, to see if those are affected by the
>>> domain_update_lock()?
>>>
>>> Xen is a bit of a twisted web; sometimes you just have to follow a web
>>> of logic around to find out what you're looking for; then, once you've
>>> come to a conclusion, test it by writing some code.
>>>
>>> For the scheduling question, you might start with looking at 
>>> vcpu_runnable().
>>>
>>> Peace,
>>>  -George
>>>
>>> >
>>> > On Wed, Nov 4, 2009 at 11:08 AM, Pankaj Parakh <me.pankajparakh@xxxxxxxxx>
>>> > wrote:
>>> >>
>>> >> So is that means there will be no interrupt loss, and also clock in
>>> >> the paused domain will be in right and expected time.. ??
>>> >>
>>> >> On Wed, Nov 4, 2009 at 12:41 AM, George Dunlap
>>> >> <george.dunlap@xxxxxxxxxxxxx> wrote:
>>> >> > If you call vcpu_pause(), it atomically increments a counter in the 
>>> >> > vcpu
>>> >> > struct.  While that counter is non-zero, the vcpu *will not* be
>>> >> > scheduled,
>>> >> > interrupts or no.  Interrupts will be delivered when it's scheduled
>>> >> > again.
>>> >> >
>>> >> > -George
>>> >> >
>>> >> > Pankaj Parakh wrote:
>>> >> >>
>>> >> >>  If I pause a vcpu/domain using those functions, say if a domain's I/O
>>> >> >> request over then its interrupt will raise and it can restart its
>>> >> >> scheduling rite..?? How this interrupts are/ can be queued so that
>>> >> >> when the vcpu is in pause state, it should nat change its state and
>>> >> >> when it come back to wait state, those interrupt will not be lost..
>>> >> >>
>>> >> >> On Tue, Nov 3, 2009 at 5:18 PM, George Dunlap
>>> >> >> <George.Dunlap@xxxxxxxxxxxxx> wrote:
>>> >> >>
>>> >> >>>
>>> >> >>> Do you mean that you want to stop one specific vcpu / domain from
>>> >> >>> being scheduled?
>>> >> >>>
>>> >> >>> If so, you're looking for the following functions:
>>> >> >>> vcpu_pause(), vcpu_unpause()
>>> >> >>> domain_pause(), domain_unpause().
>>> >> >>>
>>> >> >>> They're defined in xen/common/domain.c.
>>> >> >>>
>>> >> >>>  -George
>>> >> >>>
>>> >> >>>
>>> >> >>> On Mon, Nov 2, 2009 at 9:02 PM, Pankaj Parakh
>>> >> >>> <me.pankajparakh@xxxxxxxxx>
>>> >> >>> wrote:
>>> >> >>>
>>> >> >>>>
>>> >> >>>> Hi All,
>>> >> >>>>
>>> >> >>>> I am working on a project wherein I wanted to stop the scheduling
>>> >> >>>> activity in hypervisor through 'generic' part of scheduler, I have
>>> >> >>>> lil
>>> >> >>>> confusion as to what all things I need to mask/stop for disabling
>>> >> >>>> hypervisor to schedule any vcpu untill I want.
>>> >> >>>>
>>> >> >>>> Issues which I can think are about I/O waits or Zombie VCPUs. But 
>>> >> >>>> how
>>> >> >>>> to tackle them... I dont know..
>>> >> >>>>
>>> >> >>>> I wanted to know what all responsibility the generic scheduler holds
>>> >> >>>> in hypervisor,
>>> >> >>>>
>>> >> >>>> Any type of info or pointer can be useful.
>>> >> >>>>
>>> >> >>>> Thanks
>>> >> >>>> Pankaj Parakh
>>> >> >>>>
>>> >> >>>> _______________________________________________
>>> >> >>>> Xen-devel mailing list
>>> >> >>>> Xen-devel@xxxxxxxxxxxxxxxxxxx
>>> >> >>>> http://lists.xensource.com/xen-devel
>>> >> >>>>
>>> >> >>>>
>>> >> >>
>>> >> >>
>>> >> >>
>>> >> >>
>>> >> >
>>> >> >
>>> >>
>>> >>
>>> >>
>>> >> --
>>> >> Pankaj Parakh
>>> >
>>> >
>>> >
>>> > --
>>> > Pankaj Parakh
>>> >
>>> > _______________________________________________
>>> > Xen-devel mailing list
>>> > Xen-devel@xxxxxxxxxxxxxxxxxxx
>>> > http://lists.xensource.com/xen-devel
>>> >
>>> >
>>
>>
>>
>> --
>> Pankaj Parakh
>>
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@xxxxxxxxxxxxxxxxxxx
>> http://lists.xensource.com/xen-devel
>>
>



-- 
Pankaj Parakh

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