Re: [Xen-devel] Credit Scheduler not working correct (3.0.4-0)

[Atsushi SAKAI <sakaia@xxxxxxxxxxxxxx>]

Hi, Emmanuel

I wrote down my guess based on previous study for Timo's cases.
(I ask you this behavior is specification or not previously.)
http://lists.xensource.com/archives/html/xen-devel/2006-10/msg00365.html
This case is similar to case 2) 
(when pinned-vcpu credit sum is over 1pcpu capacity)


Let's calculate on this.
Dom1 for 100Weight
Dom2 for 200Weight 
But CPU resources is 200(2CPU x 100)
So these credits are Dom1:67 and Dom2:133
But These vcpus are pinned to pcpu0
pcpu0 has only 100. but credit total is 200.
This makes a problem.

These 2vcpu has same priority in credit scheduler,
 since it cannot not consume its credit.
So these vcpus are scheduled as round robin.
This makes equal consumption of pcpu0.

Is this wrong guess?

Thanks
Atsushi SAKAI


Emmanuel Ackaouy <ack@xxxxxxxxxxxxx> wrote:

> Ok so If I get this right, what you want to do is have 2 UP guests with
> different weights. You also want to turn off HT and you do this by
> pinning both guests on CPU 0.
> 
> Credit accounting and pinning VCPUs don't always interact well
> and I suspect you're hitting such a problem here.
> 
> If you have access to the Xen console, can you send output of
> the 'r' (runq) key while your domains are each getting 50% of
> CPU? Just take a few snapshots a few seconds apart. That would
> confirm the theory.
> 
> Also, setting cap=100 on a UP guest is pointless. Just leave it
> as zero. A VCPU isn't going to get more than 100% of a physical
> CPU anyway.
> 
> 
> On Feb 1, 2007, at 10:47, Timo Benk wrote:
> > Hi,
> >
> > on my system, it seems that the credit scheduler does not work as 
> > expected. The
> > problem seems to be related to HyperThreading, if i switch off HT in 
> > the BIOS
> > Setup, the scheduler works as expected.
> >
> > I have two domains running, both pinned to the same processor:
> >
> > Domain-0:~ # xm vcpu-list
> > Name                              ID  VCPU   CPU State   Time(s) CPU
> > Affinity
> > Domain-0                           0     0     1   ---      30.2 any 
> > cpu
> > Domain-0                           0     1     1   r--      12.0 any 
> > cpu
> > xendom1                            1     0     0   ---      98.6 0
> > xendom2                            2     0     0   r--     110.3 0
> >
> > Both domains should consume max. 100 Percent of that processor, but
> > xendom1 has a weight twice as big as xendom2:
> >
> > Domain-0:~ # xm sched-credit -d xendom1
> > {'cap': 100, 'weight': 200}
> > Domain-0:~ # xm sched-credit -d xendom2
> > {'cap': 100, 'weight': 100}
> >
> > In my understanding of the credit scheduler, xendom1 should get twice 
> > as
> > much CPU-time as xendom2. But:
> >
> > xentop - 11:05:46   Xen 3.0.4-0
> > Mem: 2612284k total, 2603852k used, 8432k free    CPUs: 2 @ 2992MHz
> >       NAME  STATE   CPU(sec) CPU(%)  [...]
> >   Domain-0 -----r         42    0.6  [...]
> >    xendom1 ------        122   49.8  [...]
> >    xendom2 -----r        133   50.2  [...]
> >
> > As you can see, both domains got an equal amount of the CPU.
> >
> > Am i missing something or do i understand something wrong?
> >
> > Greetings,
> > -timo
> > -- 
> > Timo Benk - Jabber ID: fry@xxxxxxxxxxxx - ICQ ID: #414944731
> > PGP Public Key: http://m28s01.vlinux.de/timo_benk_gpg_key.asc
> >
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel
> >
> 
> 
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