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RE: [Xen-devel] New CPU scheduler w/ SMP load balancer

To: <xen-devel@xxxxxxxxxxxxxxxxxxx>, <ack@xxxxxxxxxxxxx>
Subject: RE: [Xen-devel] New CPU scheduler w/ SMP load balancer
From: "Apparao, Padmashree K" <padmashree.k.apparao@xxxxxxxxx>
Date: Fri, 26 May 2006 11:06:54 -0700
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Thread-topic: [Xen-devel] New CPU scheduler w/ SMP load balancer
On the same note: has anyone got the same information with the BVT and
sedf schedulers:
Performance, overhead and efficiency in load balancing

- Padma

-----Original Message-----
From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Anthony
Sent: Friday, May 26, 2006 8:43 AM
To: xen-devel@xxxxxxxxxxxxxxxxxxx; ack@xxxxxxxxxxxxx
Subject: Re: [Xen-devel] New CPU scheduler w/ SMP load balancer

Hi Emmanuel,

Thanks for the heads up.  It would have been nice to float these patches

to the list before committing.

Can you provide some more details on any results you may have seen with 
the new scheduler?  How does it affect common benchmarks?  How does the 
"load balancer" scale?  How much penalty do you pay (if any at all) on

Better yet, if you have a paper you could share, that would be even 
better :-)  If you cannot share because of conference restrictions, it 
would be nice if you could a condensed version (similar to what the L4ka

group did for their afterburning work).

Based on your description though, the new scheduler looks very


Anthony Liguori

Emmanuel Ackaouy wrote:
> Executive summary
> -----------------
> I have just committed a change to xen-unstable.hg which adds
> support for a new Xen CPU scheduler, which should greatly
> enhance resource scheduling on SMP systems and provides better
> QoS controls.
> The new scheduler is not currently the default, so to enable
> it you will need to put "sched=credit" on the Xen command line.
> Please give it a go and provide us with some feedback as to how
> it performs with your workloads!
> Detail
> ------
> The new CPU scheduler automatically load balances guest VCPUs
> across all available physical CPUs on an SMP host. You no longer
> need to manually pin VCPUs to load balance the system. However,
> you can restrict which CPUs a particular VCPU may run on using
> the existing "vcpu-pin" interface.
> Each guest domain is assigned a "weight" and a "cap".
> A domain with a weight of 512 will get twice as much CPU as a
> domain with a weight of 256 on a contended host. Legal weights
> range from 1 to 65535 and the default is 256.
> The cap optionally fixes the maximum amount of CPU a guest will
> be able to consume, even if the host system has idle CPU cycles.
> The cap is expressed in percentage of one physical CPU: 100 is
> 1 physical CPU, 50 is half a CPU, 400 is 4 CPUs, etc... The
> default, 0, means there is no upper cap.
> To use the new scheduler, you need to pick up my change. You
> will need to upgrade the tools as well as the hypervisor. We
> intend to make this the default scheduler in the near future.
> Until then, you must specify "sched=credit" on the Xen command
> line in your boot loader.
> Once you are running with the new SMP credit scheduler, you will
> be able to check and modify your domains' weights and caps using
> the "xm csched" command:
> xm csched -d <domain>                 lists weight and cap
> xm csched -d <domain> -w <weight>     sets the weight
> xm csched -d <domain> -c <cap>                sets the cap
> I'm interested to hear about your experiences using this
> scheduler as well as any performance results running your
> favorite applications or benchmarks over it.
> Enjoy,
> Emmanuel.
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