Xen devel - Jan 2009 - Is anyone using the credit scheduler "cap" functionality?

I''m in the process of revising the credit scheduler design, and
I''d
like to know how important it is to maintain the "cap" functionality
of the credit scheduler.  If you use it, or know of someone who does,
could you let me know?

If you don''t know what it is, you probably aren''t using it.
:-)

Peace,
 -George

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IIRC, the cap functionality is useful primarily for application
licensing, e.g. to ensure that an app licensed for 2 cpus
never gets more than 2 cpus, even if all other cpus are idle.
I suppose it could also be used by a webhosting provider to
create similar limits to allow selling of an added-value tier
(e.g. "uncapped", kind of a poor man''s cloud computing).

Given that, I''d say this is a much too restricted forum
(primarily developers) to ask and, even if it''s not being
used today, pulling it out seems premature unless there''s
a *really* good reason.

My two cents,
Dan
> -----Original Message-----
> From: George Dunlap [mailto:George.Dunlap@eu.citrix.com]
> Sent: Tuesday, January 20, 2009 12:09 PM
> To: xen-devel@lists.xensource.com
> Subject: [Xen-devel] Is anyone using the credit scheduler "cap"
> functionality?
> 
> 
> I''m in the process of revising the credit scheduler design, and
I''d
> like to know how important it is to maintain the "cap"
functionality
> of the credit scheduler.  If you use it, or know of someone who does,
> could you let me know?
> 
> If you don''t know what it is, you probably aren''t using
it. :-)
> 
> Peace,
>  -George
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
>
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>
> From: George Dunlap <George.Dunlap@eu.citrix.com>
>
> I''m in the process of revising the credit scheduler design, and
I''d
> like to know how important it is to maintain the "cap"
functionality
> of the credit scheduler.  If you use it, or know of someone who does,
> could you let me know?
>
> If you don''t know what it is, you probably aren''t using
it. :-)

Thank you George, for asking, before putting this into code ;-)

Yes, we use it at GrokThis.net for our Xen/VPS hosting services.  I  
believe this feature to be vitally important for us.  We sell, to the  
public, root access to our Xen guests.   I imagine that we have more  
guests per machine than is typical, as we must increase the NR_IRQS  
variable in the kernel (with two block devices per guest), although I  
know that Brian Carb at Unisys has stressed it more than I have, but  
only in a lab.

To the point, because we sell to the public, and because we have a  
fairly large number of guests per machine, we use the ''cap''  
functionality to assure that our systems run smoothly.   In this  
regard, the fact that we have many guests may be more important than  
the fact that we''re selling to the public.  It is not uncommon for us  
to find guests which have been misconfigured in such a way that they  
peg the guest''s available CPU.  This happens much more frequently than
customers consuming this level of CPU naturally, but we do wish to  
limit those customers as well, based on a percentage according to the  
cost of their monthly plan.

Simply, by using caps, we can assure that abusive guests do not  
interfere with those that are more well-behaved.  Prior to  
implementing the caps, we would frequently receive complaints unless  
we vigilantly and manually  baby-sat the systems and resolved these  
situations.  After implementing, even customers not knowing we had  
made changes made remarks about improved performance.   Now, we can go  
through the systems on a weekly or even monthly basis and fix the  
"problem" guests without having to baby-sit.

The issues I''ve described are less of a concern as the ratio of guests
to cpu cores reaches 1:1, but in environments where it is practical to  
have a larger ratio between these, the cpu cap can really make a big  
difference.   I understand that significant differences to the  
scheduler might possibly solve the problems I''m describing, but if  
such changes were made it would have to be throughly tested and proven  
before it replaced, on my systems, what is there currently.

--
Eric Windisch
GrokThis.net Internet Solutions

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George Dunlap wrote:
> I''m in the process of revising the credit scheduler design, and
I''d
> like to know how important it is to maintain the "cap"
functionality
> of the credit scheduler.  If you use it, or know of someone who does,
> could you let me know?
We are using it in our "BS2000 on x86" project.


Juergen

-- 
Juergen Gross                             Principal Developer
IP SW OS6                      Telephone: +49 (0) 89 636 47950
Fujitsu Siemens Computers         e-mail: juergen.gross@fujitsu-siemens.com
Otto-Hahn-Ring 6                Internet: www.fujitsu-siemens.com
D-81739 Muenchen         Company details: www.fujitsu-siemens.com/imprint.html

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Hi, George

Of course I use "cap".

Would you explain the parameter(s) in your scheduler?
(keep two or ???)

Thanks
Atsushi SAKAI


George Dunlap <George.Dunlap@eu.citrix.com> wrote:
> I''m in the process of revising the credit scheduler design, and
I''d
> like to know how important it is to maintain the "cap"
functionality
> of the credit scheduler.  If you use it, or know of someone who does,
> could you let me know?
> 
> If you don''t know what it is, you probably aren''t using
it. :-)
> 
> Peace,
>  -George
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel


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The general mechanism and interface to the new scheduler will be the
same as the old: weight, credits, &c.  Just a lot of the plumbing will
be re-worked.  It may be a big enough to start a new scheduler,
"credit2", while the kinks get worked out; we''ll see.

For those who are using cap to provide QoS: I''m going to be adding a
new feature, a complement to the "cap" feature, which would be a
"floor" or "reservation" feature.  (Haven''t thought
of a good name for
it yet.)  Just as "cap" will make sure that a given VM never uses more
than X% of a cpu, the "reservation" feature will ensure that a VM can
always get Y% of a cpu if it wants it.  It seems like this may be
closer to what you want -- guarantee a minimum QoS, but allow VMs to
use extra resources if they''re available?

At any rate, the cap feature shouldn''t be to difficult to keep, so
since people are still using it, I''ll do the bit of extra work to keep
it in the new system.  Thanks for the input, all!

Peace,
 -George

On Wed, Jan 21, 2009 at 9:30 AM, Atsushi SAKAI <sakaia@jp.fujitsu.com>
wrote:
> Hi, George
>
> Of course I use "cap".
>
> Would you explain the parameter(s) in your scheduler?
> (keep two or ???)
>
> Thanks
> Atsushi SAKAI
>
>
> George Dunlap <George.Dunlap@eu.citrix.com> wrote:
>
>> I''m in the process of revising the credit scheduler design,
and I''d
>> like to know how important it is to maintain the "cap"
functionality
>> of the credit scheduler.  If you use it, or know of someone who does,
>> could you let me know?
>>
>> If you don''t know what it is, you probably aren''t
using it. :-)
>>
>> Peace,
>>  -George
>>
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@lists.xensource.com
>> http://lists.xensource.com/xen-devel
>
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
>
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I would add another use for cap.
Sometimes it is usefull to understand how a domain behaves as a function of the
amount of CPU that is allocated to it. For example when deciding how many
applications can be consolidated on a server you may want to run some tests with
specific benchmarks controling the exact amount of CPU allocated to the domain
running the application. This allow you to predict how a domain will behave when
the amount of CPU is limited due to sharing the CPU with other domain.
The cap is very useful for this scenario. In fact, Rutgers University and HP
Labs are working on a Research Project (JustRunIt) that uses the CAP
functionality of the scheduler to test and characterize a domain behavior as a
function of the allocated CPU.

I would be very disappointed if the CAP functionality was removed from Xen
scheduler

Renato   
> -----Original Message-----
> From: xen-devel-bounces@lists.xensource.com 
> [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of 
> Dan Magenheimer
> Sent: Tuesday, January 20, 2009 12:33 PM
> To: George Dunlap; xen-devel@lists.xensource.com
> Subject: RE: [Xen-devel] Is anyone using the credit scheduler 
> "cap" functionality?
> 
> IIRC, the cap functionality is useful primarily for 
> application licensing, e.g. to ensure that an app licensed 
> for 2 cpus never gets more than 2 cpus, even if all other 
> cpus are idle.
> I suppose it could also be used by a webhosting provider to 
> create similar limits to allow selling of an added-value tier 
> (e.g. "uncapped", kind of a poor man''s cloud computing).
> 
> Given that, I''d say this is a much too restricted forum 
> (primarily developers) to ask and, even if it''s not being 
> used today, pulling it out seems premature unless there''s a 
> *really* good reason.
> 
> My two cents,
> Dan
> 
> > -----Original Message-----
> > From: George Dunlap [mailto:George.Dunlap@eu.citrix.com]
> > Sent: Tuesday, January 20, 2009 12:09 PM
> > To: xen-devel@lists.xensource.com
> > Subject: [Xen-devel] Is anyone using the credit scheduler
"cap"
> > functionality?
> > 
> > 
> > I''m in the process of revising the credit scheduler design,
and I''d
> > like to know how important it is to maintain the "cap" 
> functionality 
> > of the credit scheduler.  If you use it, or know of someone 
> who does, 
> > could you let me know?
> > 
> > If you don''t know what it is, you probably aren''t
using it. :-)
> > 
> > Peace,
> >  -George
> > 
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.xensource.com
> > http://lists.xensource.com/xen-devel
> >
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
> 
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