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Re: [Xen-devel] planned csched improvements?

On Tue, 20 Oct 2009 10:37:19 +0100
George Dunlap <George.Dunlap@xxxxxxxxxxxxx> wrote:

> On Tue, Oct 20, 2009 at 1:01 AM, Mukesh Rathor
> <mukesh.rathor@xxxxxxxxxx> wrote:
> > Yeah, I've been thinking in the back of my mind, some sort of
> > multiple runqueus
> There already are multiple runqueues; the overhead comes from the
> "steal work" method of moving vcpus between them, which works fine for
> low number of cpus but doesn't scale well.

Exactly, we'd have to study to find the contentions and address those.
Hopefully I can take what you got, tinker around a bit, and send the
changes to see what you think.

> Hmm, I thought I had written up my plans for load-balancing in an
> e-mail to the list, but I can't seem to find them now.  Standby
> sometime for a description. :-)

Actually, I think you posted it on the list and I saved it somewhere, 
and plan on reading and figuring it once I get closer to doing the work.

> > Agree. I'm hoping to collect all that information over the next
> > couple/few months. ÂThe last attempt, made a year ago, didn't yield
> > in a whole lot of information because of problems with 32bit tools
> > and 64bit guest apps interaction.
> I have some good tools for collecting scheduling activity and
> analyzing using xentrace and xenalyze.  When you get things set up,
> let me know and I'll post some information about using xentrace /
> xenalyze to characterize a workload's scheduling.

Great thanks.

> > In a nutshell, there's tremendous smarts in the DB, and so I think
> > it prefers a simplified schedular/OS that it can provide hints to
> > and interact a little with. ÂIdeally, it would like ability for a
> > privileged thread to tell the OS/hyp, I want to yield cpu to thread
> > #xyz.
> If the thread is not scheduled on a vcpu by the OS, then when the DB
> says to yield to that thread, the OS can switch on the running vcpu,
> no changes needed.
> The only potential modification would be if the DB wants to yield to a
> thread which is scheduled on another vcpu, but that vcpu is not
> currently running.  Then the guest OS *may* want to be able to ask the
> HV to yield the currently running vcpu to the other vcpu.  That
> interface is work thinking about.

Yup, precisely.

> > Moreover, my focus is large, 32 to 128 logical processors, with 1/2
> > to 1TB memory. ÂAs such, I also want to address VCPUs being confined
> > to logical block of physical CPUs, taking into consideration that
> > licenses are per physical cpu core.
> This sounds like it would benefit from the "CPU pools" patch submitted
> by Juergen Gross.
 Yes, I saw that also on the list also, and when I get closer to doing the
 work, will take a closer look. Right now I am still trying to round up
 the hardware, then will have to round up folks familiar with benchmarks
 to setup them up. Then the easier part begins :)...


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