From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Xu Subject: Re: performance of credit2 on hybrid workload Date: Tue, 31 May 2011 20:55:16 -0400 Message-ID: References: <1306340309.21026.8524.camel@elijah> <1306401493.21026.8526.camel@elijah> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============1354943781==" Return-path: In-Reply-To: <1306401493.21026.8526.camel@elijah> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: George Dunlap , xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org --===============1354943781== Content-Type: multipart/alternative; boundary=20cf3005149250989504a49bf969 --20cf3005149250989504a49bf969 Content-Type: text/plain; charset=ISO-8859-1 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 > 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 > > > > 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 > > > > > > > > > --20cf3005149250989504a49bf969 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Hi,

I want to reduce the latency of a specific VM. How s= hould I do based on credit scheduler? For example, I will add another param= eter latency besides weight and cap, and schedule the = vcpu whose VM holds the least latency firstly each time.=A0Thanks.

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.

=A0-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<= br> > 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<= br> > 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>
>
> =A0 =A0 =A0 =A0 On Mon, 2011-05-23 at 09:15 +0100, David Xu wrote:
> =A0 =A0 =A0 =A0 > Hi,
> =A0 =A0 =A0 =A0 >
> =A0 =A0 =A0 =A0 >
> =A0 =A0 =A0 =A0 > Xen4.1 datasheet tells that credit2 scheduler is = designed
> =A0 =A0 =A0 =A0 for latency
> =A0 =A0 =A0 =A0 > sensitive workloads. Does it have some improvemen= t on the
> =A0 =A0 =A0 =A0 hybrid
> =A0 =A0 =A0 =A0 > workload including both the cpu-bound and latency= -sensitive
> =A0 =A0 =A0 =A0 i/o work?
> =A0 =A0 =A0 =A0 > For example, if a VM runs a cpu-bound task burnin= g the cpu
> =A0 =A0 =A0 =A0 and a
> =A0 =A0 =A0 =A0 > i/o-bound (latency-sensitive) task simultaneously= , will the
> =A0 =A0 =A0 =A0 latency be
> =A0 =A0 =A0 =A0 > guaranteed? And how?
>
>
> =A0 =A0 =A0 =A0 At the moment, the "mixed workload" problem,= where a single VM
> =A0 =A0 =A0 =A0 does both
> =A0 =A0 =A0 =A0 cpu-intensive and latency-sensitive* workloads, has no= t been
> =A0 =A0 =A0 =A0 addressed
> =A0 =A0 =A0 =A0 yet. =A0I have some ideas, but I haven't implement= ed them yet.
>
> =A0 =A0 =A0 =A0 * i/o-bound is not the same as latency sensitive. =A0T= hey
> =A0 =A0 =A0 =A0 obviously go
> =A0 =A0 =A0 =A0 together frequently, but I would make a distinction be= tween
> =A0 =A0 =A0 =A0 them. =A0For
> =A0 =A0 =A0 =A0 example, an scp (copy over ssh) can easily become cpu-= bound if
> =A0 =A0 =A0 =A0 there is
> =A0 =A0 =A0 =A0 competition for the cpu -- but it is nonetheless laten= cy
> =A0 =A0 =A0 =A0 sensitive. =A0(I
> =A0 =A0 =A0 =A0 guess to put it another way, a workload which is
> =A0 =A0 =A0 =A0 latency-sensitive may
> =A0 =A0 =A0 =A0 become i/o-bound if its scheduling latency is too high= .)
>
> =A0 =A0 =A0 =A0 =A0-George
>
>
>



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