What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin" and "dom0_max_vcpus=4" ?

What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin" and "dom0_max_vcpus=4" ?

[lei yang]

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Hi experts,


Q1:What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin" and
"dom0_max_vcpus=4" ?
which will get better performance

Q2: dom0_max_vcpus=4 means "core0-3 will be just used by dom0" or means "4
cores(not dedicate cores) will be used by dom0, eg: core2-5 or core3-6?

Q3.what does mean "nosmp" , xen, dom0,domU, will just use one core????if so,
can we specify the use different core. eg: dom0=core2 domU=core3? xen will
use just one core?

Thanks
Lei








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"We learn from failure, not from success!"

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Re: What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin" and "dom0_max_vcpus=4" ?

[Keir Fraser]

On 21/05/2010 04:09, "lei yang" <yanglei.fage@gmail.com> wrote:

> Hi experts,
> 
> 
> Q1:What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin" and 
> "dom0_max_vcpus=4" ? which will get better performance

The former restricts Xen to only run Dom0 VCPUs 0-3 on physical CPUs 0-3.
It's not really a performance thing, but instead is to mean that some things
like cpufreq management can work directly from dom0. We don't really use the
dom0_vcpus_pin option much.

> Q2: dom0_max_vcpus=4 means "core0-3 will be just used by dom0" or means "4
> cores(not dedicate cores) will be used by dom0, eg: core2-5 or core3-6?

Dom0's VCPUs can be scheduled on any physical CPU at any time, unles
dom0_vcpus_pin is specified.

> Q3.what does mean "nosmp" , xen, dom0,domU, will just use one core????if so,
> can we specify the use different core. eg: dom0=core2 domU=core3? xen will use
> just one core?

It brings Xen up on the boot CPU only. Nothing in the system will use the
other CPUs. You don't want to use this option really.

 -- Keir

RE: What's the different for "dom0_max_vcpus=4dom0_vcpus_pin" and "dom0_max_vcpus=4" ?

[Robert Dunkley]

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Hi Lei,

 

 

Q1: The pin is needed to lock Dom0 to cores 0 & 1.

 

Q2: It means 4 vcpus are allocated to Dom0, they can float between
physical cores. VCPUs don't really line up with cores, you can assign 8
vcpus on a DomU  on a 4 core Dom0 box for example. 8 cpus will appear in
the VM but Xen will try to allocate the request within its 4 physucal
cores. Generally assigning more VPUs than you have physical cores is
pointless.

 

Q3: No SMP for a DOMU will mean the kernel is not SMP aware, this can
save a small amount of overhead and improve scheduling in certain cases
on a single core DOMU. I'm not sure what the affect would be on Dom0, my
guess is it won't be good.

 

 

 

Rob

 

From: xen-users-bounces@lists.xensource.com
[mailto:xen-users-bounces@lists.xensource.com] On Behalf Of lei yang
Sent: 21 May 2010 04:09
To: Xen Mailing List; xen-devel@lists.xensource.com
Subject: [Xen-users] What's the different for
"dom0_max_vcpus=4dom0_vcpus_pin" and "dom0_max_vcpus=4" ?

 

Hi experts,


Q1:What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin" and
"dom0_max_vcpus=4" ?
which will get better performance

Q2: dom0_max_vcpus=4 means "core0-3 will be just used by dom0" or means
"4 cores(not dedicate cores) will be used by dom0, eg: core2-5 or
core3-6?

Q3.what does mean "nosmp" , xen, dom0,domU, will just use one core????if
so, can we specify the use different core. eg: dom0=core2 domU=core3?
xen will use just one core?

Thanks
Lei








-- 
"We learn from failure, not from success!"


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Re: What's the different for "dom0_max_vcpus=4dom0_vcpus_pin" and "dom0_max_vcpus=4" ?

[lei yang]

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On Fri, May 21, 2010 at 8:02 PM, Robert Dunkley <Robert@saq.co.uk> wrote:

>  Hi Lei,
>
>
>
>
>
> Q1: The pin is needed to lock Dom0 to cores 0 & 1.
>
>
>
dom0_max_vcpus=4 dom0_vcpus_pin just lock Dom0 to cores0 and 1?? but it's
"4"


>  Q2: It means 4 vcpus are allocated to Dom0, they can float between
> physical cores.
>

dom0_max_vcpus=4 , can be the 4 cores=2 3 4 5, does it will change to 1 2 3
4? or just bind to 2 3 4 5
dom0_max_vcpus=4 dom0_vcpus_pin will just to core0-3?

>  VCPUs don’t really line up with cores, you can assign 8 vcpus on a DomU
>  on a 4 core Dom0 box for example. 8 cpus will appear in the VM but Xen will
> try to allocate the request within its 4 physucal cores. Generally assigning
> more VPUs than you have physical cores is pointless.
>
>
>
> Q3: No SMP for a DOMU will mean the kernel is not SMP aware, this can save
> a small amount of overhead and improve scheduling in certain cases on a
> single core DOMU. I’m not sure what the affect would be on Dom0, my guess is
> it won’t be good.
>
>
>
>
>
>
>
> Rob
>
>
>
> *From:* xen-users-bounces@lists.xensource.com [mailto:
> xen-users-bounces@lists.xensource.com] *On Behalf Of *lei yang
> *Sent:* 21 May 2010 04:09
> *To:* Xen Mailing List; xen-devel@lists.xensource.com
> *Subject:* [Xen-users] What's the different for
> "dom0_max_vcpus=4dom0_vcpus_pin" and "dom0_max_vcpus=4" ?
>
>
>
> Hi experts,
>
>
> Q1:What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin" and
> "dom0_max_vcpus=4" ?
> which will get better performance
>
> Q2: dom0_max_vcpus=4 means "core0-3 will be just used by dom0" or means "4
> cores(not dedicate cores) will be used by dom0, eg: core2-5 or core3-6?
>
> Q3.what does mean "nosmp" , xen, dom0,domU, will just use one core????if
> so, can we specify the use different core. eg: dom0=core2 domU=core3? xen
> will use just one core?
>
> Thanks
> Lei
>
>
>
>
>
>
>
>
> --
> "We learn from failure, not from success!"
>
> **
>
> *The SAQ Group*
>
> *Registered Office: 18 Chapel Street, Petersfield, Hampshire GU32 3DZ*
> SAQ is the trading name of SEMTEC Limited. Registered in England & Wales
> Company Number: 06481952
>
>
>
> http://www.saqnet.co.uk AS29219
>
> SAQ Group Delivers high quality, honestly priced communication and I.T.
> services to UK Business.
>
> Broadband : Domains : Email : Hosting : CoLo : Servers : Racks : Transit :
> Backups : Managed Networks : Remote Support.
>
>
>
>  [image: SAQ Group]
>
>
>
> *ISPA Member*
>



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Re: What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin" and "dom0_max_vcpus=4" ?

[lei yang]

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On Fri, May 21, 2010 at 2:57 PM, Keir Fraser <keir.fraser@eu.citrix.com>wrote:

> On 21/05/2010 04:09, "lei yang" <yanglei.fage@gmail.com> wrote:
>
> > Hi experts,
> >
> >
> > Q1:What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin" and
> > "dom0_max_vcpus=4" ? which will get better performance
>
> The former restricts Xen to only run Dom0 VCPUs 0-3 on physical CPUs 0-3.
>

dom0_max_vcpus=4 dom0_vcpus_pin will just to core0-3? can it be 3 4 5 6?
if remove "dom0_vcpus_pin" just use "  dom0_max_vcpus=4 " can it be 3 4 5 6
?


> It's not really a performance thing, but instead is to mean that some
> things
> like cpufreq management can work directly from dom0. We don't really use
> the
> dom0_vcpus_pin option much.
>
> > Q2: dom0_max_vcpus=4 means "core0-3 will be just used by dom0" or means
> "4
> > cores(not dedicate cores) will be used by dom0, eg: core2-5 or core3-6?
>
> Dom0's VCPUs can be scheduled on any physical CPU at any time, unles
> dom0_vcpus_pin is specified.
>
> > Q3.what does mean "nosmp" , xen, dom0,domU, will just use one core????if
> so,
> > can we specify the use different core. eg: dom0=core2 domU=core3? xen
> will use
> > just one core?
>
> It brings Xen up on the boot CPU only. Nothing in the system will use the
> other CPUs. You don't want to use this option really.
>
>  -- Keir
>
>
>


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Re: What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin" and "dom0_max_vcpus=4" ?

[Pasi Kärkkäinen]

On Fri, May 21, 2010 at 11:39:50PM +0800, lei yang wrote:
>    On Fri, May 21, 2010 at 2:57 PM, Keir Fraser
>    <[1]keir.fraser@eu.citrix.com> wrote:
> 
>      On 21/05/2010 04:09, "lei yang" <[2]yanglei.fage@gmail.com> wrote:
> 
>      > Hi experts,
>      >
>      >
>      > Q1:What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin" and
>      > "dom0_max_vcpus=4" ? which will get better performance
> 
>      The former restricts Xen to only run Dom0 VCPUs 0-3 on physical CPUs
>      0-3.
> 
> 
>    dom0_max_vcpus=4 dom0_vcpus_pin will just to core0-3?
>

Yes.

> can it be 3 4 5 6?
>

Yes, modify the pinning when the system has booted up using "xm vcpu-pin".

>    if remove "dom0_vcpus_pin" just use "  dom0_max_vcpus=4 " can it be 3 4 5
>    6 ?
> 

Yes, set up the pinning yourself.

-- Pasi

> 
>      It's not really a performance thing, but instead is to mean that some
>      things
>      like cpufreq management can work directly from dom0. We don't really use
>      the
>      dom0_vcpus_pin option much.
>      > Q2: dom0_max_vcpus=4 means "core0-3 will be just used by dom0" or
>      means "4
>      > cores(not dedicate cores) will be used by dom0, eg: core2-5 or
>      core3-6?
> 
>      Dom0's VCPUs can be scheduled on any physical CPU at any time, unles
>      dom0_vcpus_pin is specified.
>      > Q3.what does mean "nosmp" , xen, dom0,domU, will just use one
>      core????if so,
>      > can we specify the use different core. eg: dom0=core2 domU=core3? xen
>      will use
>      > just one core?
> 
>      It brings Xen up on the boot CPU only. Nothing in the system will use
>      the
>      other CPUs. You don't want to use this option really.
>       -- Keir
> 
>    --
>    "We learn from failure, not from success!"
> 
> References
> 
>    Visible links
>    1. mailto:keir.fraser@eu.citrix.com
>    2. mailto:yanglei.fage@gmail.com

> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel

Re: What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin" and "dom0_max_vcpus=4" ?

[lei yang]

[-- Attachment #1.1: Type: text/plain, Size: 2688 bytes --]

On Fri, May 21, 2010 at 11:46 PM, Pasi Kärkkäinen <pasik@iki.fi> wrote:

> On Fri, May 21, 2010 at 11:39:50PM +0800, lei yang wrote:
> >    On Fri, May 21, 2010 at 2:57 PM, Keir Fraser
> >    <[1]keir.fraser@eu.citrix.com> wrote:
> >
> >      On 21/05/2010 04:09, "lei yang" <[2]yanglei.fage@gmail.com> wrote:
> >
> >      > Hi experts,
> >      >
> >      >
> >      > Q1:What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin" and
> >      > "dom0_max_vcpus=4" ? which will get better performance
> >
> >      The former restricts Xen to only run Dom0 VCPUs 0-3 on physical CPUs
> >      0-3.
> >
> >
> >    dom0_max_vcpus=4 dom0_vcpus_pin will just to core0-3?
> >
>
> Yes.
>
> > can it be 3 4 5 6?
> >
>
> Yes, modify the pinning when the system has booted up using "xm vcpu-pin".
>
>

if I don't use "xm vcpu-pin" does it will use core 0 1 2 3 by default not
can use 3 4 5 6?
if so, does core 0-4 just can used by dom0? domU can't use it?

Thanks
Lei


> >    if remove "dom0_vcpus_pin" just use "  dom0_max_vcpus=4 " can it be 3
> 4 5
> >    6 ?
> >
>
> Yes, set up the pinning yourself.
>
>
again. if just use "dom0_max_vcpus=4" not use "dom0_vcpus_pin"  and I don't
use "xm vcpu-pin", can 't be 3 4 5 6,

Thanks
Lei


> -- Pasi
>
> >
> >      It's not really a performance thing, but instead is to mean that
> some
> >      things
> >      like cpufreq management can work directly from dom0. We don't really
> use
> >      the
> >      dom0_vcpus_pin option much.
> >      > Q2: dom0_max_vcpus=4 means "core0-3 will be just used by dom0" or
> >      means "4
> >      > cores(not dedicate cores) will be used by dom0, eg: core2-5 or
> >      core3-6?
> >
> >      Dom0's VCPUs can be scheduled on any physical CPU at any time, unles
> >      dom0_vcpus_pin is specified.
> >      > Q3.what does mean "nosmp" , xen, dom0,domU, will just use one
> >      core????if so,
> >      > can we specify the use different core. eg: dom0=core2 domU=core3?
> xen
> >      will use
> >      > just one core?
> >
> >      It brings Xen up on the boot CPU only. Nothing in the system will
> use
> >      the
> >      other CPUs. You don't want to use this option really.
> >       -- Keir
> >
> >    --
> >    "We learn from failure, not from success!"
> >
> > References
> >
> >    Visible links
> >    1. mailto:keir.fraser@eu.citrix.com
> >    2. mailto:yanglei.fage@gmail.com
>
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.xensource.com
> > http://lists.xensource.com/xen-devel
>
>


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Re: What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin" and "dom0_max_vcpus=4" ?

[Pasi Kärkkäinen]

On Fri, May 21, 2010 at 11:51:34PM +0800, lei yang wrote:
>    On Fri, May 21, 2010 at 11:46 PM, Pasi Kärkkäinen <[1]pasik@iki.fi> wrote:
> 
>      On Fri, May 21, 2010 at 11:39:50PM +0800, lei yang wrote:
>      >    On Fri, May 21, 2010 at 2:57 PM, Keir Fraser
>      >    <[1][2]keir.fraser@eu.citrix.com> wrote:
>      >
>      >      On 21/05/2010 04:09, "lei yang" <[2][3]yanglei.fage@gmail.com>
>      wrote:
>      >
>      >      > Hi experts,
>      >      >
>      >      >
>      >      > Q1:What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin"
>      and
>      >      > "dom0_max_vcpus=4" ? which will get better performance
>      >
>      >      The former restricts Xen to only run Dom0 VCPUs 0-3 on physical
>      CPUs
>      >      0-3.
>      >
>      >
>      >    dom0_max_vcpus=4 dom0_vcpus_pin will just to core0-3?
>      >
> 
>      Yes.
>      > can it be 3 4 5 6?
>      >
> 
>      Yes, modify the pinning when the system has booted up using "xm
>      vcpu-pin".
> 
> 
> 
>    if I don't use "xm vcpu-pin" does it will use core 0 1 2 3 by default not
>    can use 3 4 5 6?
>

Yes, it'll use 0 1 2 3 as a default. It cannot be changed, unless you do 
custom pinning after the system has started.

>    if so, does core 0-4 just can used by dom0? domU can't use it?
> 

domU can (and will) use them, so you need to also pin the domUs so that they won't
try to use the dom0 cores, if you absolutely want to dedicate 4 cores only for dom0.

Just play with "xm vcpu-pin" and "xm vcpu-list" and you'll figure it out.

-- Pasi

>    Thanks
>    Lei
> 
> 
>      >    if remove "dom0_vcpus_pin" just use "  dom0_max_vcpus=4 " can it be
>      3 4 5
>      >    6 ?
>      >
> 
>      Yes, set up the pinning yourself.
> 
> 
>    again. if just use "dom0_max_vcpus=4" not use "dom0_vcpus_pin"  and I
>    don't use "xm vcpu-pin", can 't be 3 4 5 6,
> 
>    Thanks
>    Lei
> 
> 
>      -- Pasi
>      >
>      >      It's not really a performance thing, but instead is to mean that
>      some
>      >      things
>      >      like cpufreq management can work directly from dom0. We don't
>      really use
>      >      the
>      >      dom0_vcpus_pin option much.
>      >      > Q2: dom0_max_vcpus=4 means "core0-3 will be just used by dom0"
>      or
>      >      means "4
>      >      > cores(not dedicate cores) will be used by dom0, eg: core2-5 or
>      >      core3-6?
>      >
>      >      Dom0's VCPUs can be scheduled on any physical CPU at any time,
>      unles
>      >      dom0_vcpus_pin is specified.
>      >      > Q3.what does mean "nosmp" , xen, dom0,domU, will just use one
>      >      core????if so,
>      >      > can we specify the use different core. eg: dom0=core2
>      domU=core3? xen
>      >      will use
>      >      > just one core?
>      >
>      >      It brings Xen up on the boot CPU only. Nothing in the system will
>      use
>      >      the
>      >      other CPUs. You don't want to use this option really.
>      >       -- Keir
>      >
>      >    --
>      >    "We learn from failure, not from success!"
>      >
>      > References
>      >
>      >    Visible links
>      >    1. mailto:[4]keir.fraser@eu.citrix.com
>      >    2. mailto:[5]yanglei.fage@gmail.com
>      > _______________________________________________
>      > Xen-devel mailing list
>      > [6]Xen-devel@lists.xensource.com
>      > [7]http://lists.xensource.com/xen-devel
> 
>    --
>    "We learn from failure, not from success!"
> 
> References
> 
>    Visible links
>    1. mailto:pasik@iki.fi
>    2. mailto:keir.fraser@eu.citrix.com
>    3. mailto:yanglei.fage@gmail.com
>    4. mailto:keir.fraser@eu.citrix.com
>    5. mailto:yanglei.fage@gmail.com
>    6. mailto:Xen-devel@lists.xensource.com
>    7. http://lists.xensource.com/xen-devel

Re: [Xen-devel] What's the different for "dom0_max_vcpus=4 dom0_vcpus_pin" and "dom0_max_vcpus=4" ?

[Keir Fraser]

On 21/05/2010 16:39, "lei yang" <yanglei.fage@gmail.com> wrote:

>> The former restricts Xen to only run Dom0 VCPUs 0-3 on physical CPUs 0-3.
>  
> dom0_max_vcpus=4 dom0_vcpus_pin will just to core0-3? can it be 3 4 5 6?
> if remove "dom0_vcpus_pin" just use "  dom0_max_vcpus=4 " can it be 3 4 5 6 ?

No, but you can set whatever affinity you like after dom0 has booted. For
example, to pin Dom0 VCPUs 0-3 to CPUs 3-6 respectively:
xl vcpu-pin 0 0 3
xl vcpu-pin 0 1 4
xl vcpu-pin 0 2 5
xl vcpu-pin 0 3 6
(or use xm vcpu-pin if you are not using the new xl command).

 -- Keir