Re: [Xen-devel] LONG: An Asymmetric-Aware Scheduler for Hypervisor

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Sat, Aug 27, 2011 at 01:05:55AM +0530, Nilesh Somani wrote:
> *         Topic: *Description on How to make the scheduler of Hypervisor
> asymmetric aware.
> 
>         The processor's have evolved from single-core to multi-core
> processors. But these Processors
> have been Symmetric ie identical.Every day the data on web in increasing and
> the companies need
> to set up large and powerful data center's. The power consumption is thus
> increasing to a large extent.
> Even as the requests on web increase the number of core's also need to
> increased to speed up the
> processing in large data center's. But with increasing number of cores the
> power consumption is also
> increasing.
>         If the application has less Instruction level parallelism then its
> latency on high core processor that
> supports high level of parallelism increases with power consumption. So to
> deal with these situations
> came Asymmetric Multi core Processors.
>        These are processor's with some fast cores and some slow cores. Now
> the application requiring
> low ILP can run on slow cores thus reducing the latency and the power
> consumption. The area required
> for 4 fast cores can have 2 fast cores and 6 small cores. The performance
> increase in multithreading
> is anytime more on 8 cores(2-fast and 6-slow) rather than 4 fast cores.
>         What I came up in a paper is that the hypervisor's today are
> asymmetric unaware. Thus for every
> request it gets it treats all the processor's identical even in asymmetric
> hardware. Consider IBM
> Blade Server QS series server that has 2 cell processors of 3.2 GHz. This
> means there are 2 fast cores
> and 16 slow cores compared to the fast ones. It might happen that the
> request to hypervisor is for fast
> core but suppose both the fast cores are not idle and as the hypervisor
> treats all the cores one and the same
> it might transfer the request to slow core which is not desired.
>        So to deal with such situations and to improve the efficiency in
> power i propose to modify the scheduler
> of the Xen hypervisor and make it asymmetric aware to schedule the jobs
> properly ie in a manner to increase
> the overall efficiency. Care also needs to be taken that the fast cores dont
> go idle before the slow cores to
> increase the efficiency and performance. Also there should be fairness among
> the jobs requesting fast or
> slow cores. We can also assign priorities to VM's such that the requests
> from a particular VM goes to either
> fast or slow cores.
> 
> I had some doubts regarding this.
> I went through some IEEE and ASM papers and there has been proposals to make
> schedulers aware of AMPs. So why hasn't it not yet being implemented in Xen?
> Are there any issues?
> Is there any other hardware other than Cell processor to go on with the
> idea?
> 

The first problem is that Xen hasn't been ported to PPC/Cell.
(http://wiki.xensource.com/xenwiki/XenPPC)

Are there Asymmetric x86/x64 systems out there?

-- Pasi


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