Re: performance of credit2 on hybrid workload

[David Xu <davidxu06@gmail.com>]

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Hi,

I want to reduce the latency of a specific VM. How should I do based on
credit scheduler? For example, I will add another parameter *latency*besides
*weight *and *cap, *and schedule the vcpu whose VM holds the least latency
firstly each time. Thanks.

Regards,
Cong

2011/5/26 George Dunlap <george.dunlap@citrix.com>

> Please reply to the list. :-)
>
> Also, this is a question about credit1, so it should arguably be a
> different thread.
>
>  -George
>
> On Wed, 2011-05-25 at 19:34 +0100, David Xu wrote:
> > Thanks. The boost mechanism in credit can significantly reduce the
> > scheduling latency for pure I/O workload. Since the minimum interval
> > of credit scheduling is 10ms, the magnitude of latency for the target
> > VM should be 10ms (except the credit is not used up and vcpu remain
> > the head of runqueue ) as well. Why the real latency in my test (Ping
> > the target VM) is much shorter than 10ms? Does the vcpu of target VM
> > remain the head of runqueue if it was boosted?
> >
> >
> > David
> >
> > 2011/5/25 George Dunlap <george.dunlap@citrix.com>
> >
> >         On Mon, 2011-05-23 at 09:15 +0100, David Xu wrote:
> >         > Hi,
> >         >
> >         >
> >         > Xen4.1 datasheet tells that credit2 scheduler is designed
> >         for latency
> >         > sensitive workloads. Does it have some improvement on the
> >         hybrid
> >         > workload including both the cpu-bound and latency-sensitive
> >         i/o work?
> >         > For example, if a VM runs a cpu-bound task burning the cpu
> >         and a
> >         > i/o-bound (latency-sensitive) task simultaneously, will the
> >         latency be
> >         > guaranteed? And how?
> >
> >
> >         At the moment, the "mixed workload" problem, where a single VM
> >         does both
> >         cpu-intensive and latency-sensitive* workloads, has not been
> >         addressed
> >         yet.  I have some ideas, but I haven't implemented them yet.
> >
> >         * i/o-bound is not the same as latency sensitive.  They
> >         obviously go
> >         together frequently, but I would make a distinction between
> >         them.  For
> >         example, an scp (copy over ssh) can easily become cpu-bound if
> >         there is
> >         competition for the cpu -- but it is nonetheless latency
> >         sensitive.  (I
> >         guess to put it another way, a workload which is
> >         latency-sensitive may
> >         become i/o-bound if its scheduling latency is too high.)
> >
> >          -George
> >
> >
> >
>
>
>

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