Hi George,
First of all I want to thank you, I am able to run that rr scheduler,
wake function was the only problem which was stopping it to run, I
still need to improve it. Your review was very very helpful. Also now
I have two machine serial console setup which let me see printk s in
XEN code.
Now I want to manipulate a parameter of policy say quantum of
timeslice in runtime. I am unable to find much reference for it. I
know that I have to make a entry in domctl.h but what next..
Please guide me through.
Thanks a lot again.
Regards,
Pankaj Parakh.
On Mon, Oct 26, 2009 at 8:56 PM, George Dunlap
<george.dunlap@xxxxxxxxxxxxx> wrote:
>
> Pankaj Parakh wrote:
>>
>> Hi George,
>>
>> Thanks for showing interest, First of all I'll try to setup debugging
>> environment for Xen, I also checked the mailing list of Ananth also I
>> know him personally, he has left it some where in middle.
>>
>> I tried printk's and locking method to find out which function is
>> being called in schedule.c, I found the following sequence:-
>>
>> schedule_init()
>> schedule_domain_init()
>> schedule_vcpu_init()
>> schedule_domain_init()
>> schedule_vcpu_init()
>> (from here no function is called from schedule.c, but system hangs)
>>
>> I cant say what the problem is, I am only changing the sched_priv data
>> of vcpu struct, also my rr sched has only three functions viz
>> init_vcpu, destroy_vcpu, do_schedule.
>>
>> I have attached the code as well.
>>
>> Following are my doubts:
>>
>
> [Language point: In many English dialects, such as US and UK, "doubt" implies
> something negative. To avoid being misunderstood by speakers of those
> dialects, "questions" might be a better word to use.]
>>
>> 1. Is the above function sequence is right ? Why two times init_domain
>> is called during the boot.
>>
>
> I suspect that the idle domain (32727) and domain 0 are the two domains being
> initialized. You could easily find out by adding the domain id to the printk.
>>
>> 2. Do a scheduler policy need to manipulate other part of vcpu struct
>> (other than sched_priv)
>>
>
> I don't believe so. You could look through other schedulers (like the credit
> scheduler) to see if this is so.
>>
>> 3. Is it necessary to maintain domain information inside scheduler policy
>>
>
> I don't know.
>
> A quick scan through the attached file turn up a couple of points:
> + It appears that the algorithm adds *all* vcpus to a single global runqueue,
> and scans through them looking for "runnable" vcpus on schedule. This seems
> pretty pointless: why not add them to the global runqueue on wake?
> + Furthermore, I'm not sure your linked-list implementation is sound; for
> example, the initial v->sched_priv is not initialized to NULL. (Not going to
> spend a lot of time trying to figure out if that's OK or not.)
> + There is some missing logic regarding the v->processor field and
> sync_vcpu_execstate(). Xen is designed expecting a per-cpu runqueue with
> explicit migrations of vcpus between pcpus. One of the reasons for this is
> so that when switching between a vcpu and the idle domain, it doesn't
> actually need to do a full context switch. As a result, if you run a vcpu on
> one cpu, and then run it on another without an explicit sync, you may have
> stale data in the vcpu struct (and Xen will throw a BUG).
> + You don't implement a .wake() method. I think that Xen will wake() dom0
> when it's ready, expecting the .wake() method to raise a SCHEDULE softirq on
> the appropriate pcpu (from which the .do_schedule() method is called). So no
> wake method means no schedule(), and no schedule means it just runs the idle
> domain.
>
> It might be best to start with just one pcpu, and adding multiple cpus once
> you get things running. Try adding a wake() method that will check to see if
> cpu 0 is idle; if it is, raise SCHEDULE_SOFTIRQ on that cpu, and see what you
> get. After that, try adding some logic to figure out which other cpu to wake
> instead; but be advised that you'll probably hit the BUG() relating to
> sync_vcpu_execstate() not being properly called.
>
> -George
>>
>> On Tue, Oct 13, 2009 at 5:17 PM, George Dunlap
>> <George.Dunlap@xxxxxxxxxxxxx> wrote:
>>
>>>
>>> Pankaj,
>>>
>>> I haven't used the round-robin scheduler code in that book, but
>>> another guy named Ananth tried to use it unsuccessfully as well. You
>>> can see some of that thread here (not sure why I can't find the
>>> original post):
>>> http://lists.xensource.com/archives/html/xen-devel/2009-05/msg00004.html
>>>
>>> Most of us are not so interested in finding the bug in the books'
>>> code, but we are interested in helping *you* find it. If you continue
>>> to do hypervisor work (and especially if you do anything with the
>>> scheduler), you're going to have to learn how to debug a hypervisor,
>>> which is often rather a pain in the neck.
>>>
>>> There is some advice in the thread linked to above about setting up a
>>> serial console. You can add printk()'s around to find out what the
>>> sched_rr code is doing and where it's going wrong, and ask more
>>> questions on the list if you get stuck. (Feel free to cc me to bring
>>> it to my attention, but always send it to the whole list.)
>>>
>>> Good luck,
>>> -George
>>>
>>>
>>> On Mon, Oct 12, 2009 at 6:15 PM, Pankaj Parakh
>>> <me.pankajparakh@xxxxxxxxx> wrote:
>>>
>>>>
>>>> Hi All,
>>>>
>>>> I am trying to learn about schedulers of XEN, so for a start I am
>>>> using XEN 3.4.0 and using book - The Definitive Guide to the Xen
>>>> Hypervisor - by David Chisnall, I have followed its steps to add
>>>> scheduler which is there in Chap. 12
>>>> But I dont know what is the problem, I am unable to boot with that
>>>> scheduler selected, I have been trying to debug this problem, but
>>>> kinda stuck in it.
>>>> The scheduler given in that book is a trivial round robin scheduler.
>>>>
>>>> Is the problem is with the code or with the procedure, I dont know that
>>>> also.
>>>>
>>>> Plzz help me out of this.
>>>>
>>>> Thanks
>>>> Pankaj Parakh
>>>>
>>>> _______________________________________________
>>>> Xen-devel mailing list
>>>> Xen-devel@xxxxxxxxxxxxxxxxxxx
>>>> http://lists.xensource.com/xen-devel
>>>>
>>>>
>>
>>
>>
>> --
>> Pankaj Parakh
>>
>
--
Pankaj Parakh
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