Re: Fwd: Question about Xen Console

Re: Fwd: Question about Xen Console

[Konrad Rzeszutek Wilk]

On Mon, Apr 01, 2013 at 01:59:15PM +0800, Wei Xu wrote:
> Hi Konrad,
> I'd like to consult you some questions about the Xen Console, i'm
> investigating it recently, i take some test on Linux(Fedora) hvm guest, it
> works good. (Xen-4.1.3 and Linux 3.5.0).
> 
> The most confused question of me is why did Xen Console come to mind in the
> early date, What's the requirement? Was it going to replace the emulated
> serial by qemu, or just an additional way to access the guest with high
> performance or sth other?
> 
> I have post this in the xen-devel mail list and got some useful answer,

Then lets add CC to it again.
> since you are the expert about it, I'd like to consult you for the original
> answer, thanks.

The answer is 'additional way to access the guest without having to emulate
the serial port'

> 
> Regards,
> Wei

Re: Fwd: Question about Xen Console

[Wei Xu]

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On Mon, Apr 1, 2013 at 8:47 PM, Konrad Rzeszutek Wilk <
konrad.wilk@oracle.com> wrote:

> On Mon, Apr 01, 2013 at 01:59:15PM +0800, Wei Xu wrote:
> > Hi Konrad,
> > I'd like to consult you some questions about the Xen Console, i'm
> > investigating it recently, i take some test on Linux(Fedora) hvm guest,
> it
> > works good. (Xen-4.1.3 and Linux 3.5.0).
> >
> > The most confused question of me is why did Xen Console come to mind in
> the
> > early date, What's the requirement? Was it going to replace the emulated
> > serial by qemu, or just an additional way to access the guest with high
> > performance or sth other?
> >
> > I have post this in the xen-devel mail list and got some useful answer,
>
> Then lets add CC to it again.
> > since you are the expert about it, I'd like to consult you for the
> original
> > answer, thanks.
>
> The answer is 'additional way to access the guest without having to emulate
> the serial port'
>
> Thanks.

So this will improve the performance a lot on both Dom0 and DomU side,
since the speed is not very critical when accessing a guest via console, I
guess the most important benefit is to reduce the cpu cost of dom0  when
emulating the serial port, is it or sth other?

I have talked to stefano and he told the early printk is not supported by
HVM guest while it's available for PV guest with "earlyprintk=xen"
indicated in kernel boot up parameters, so is there any concern to support
it in the future? or is this worth to do?

> Regards,

> > Wei
>

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Re: Fwd: Question about Xen Console

[Konrad Rzeszutek Wilk]

On Mon, Apr 01, 2013 at 09:16:04PM +0800, Wei Xu wrote:
> On Mon, Apr 1, 2013 at 8:47 PM, Konrad Rzeszutek Wilk <
> konrad.wilk@oracle.com> wrote:
> 
> > On Mon, Apr 01, 2013 at 01:59:15PM +0800, Wei Xu wrote:
> > > Hi Konrad,
> > > I'd like to consult you some questions about the Xen Console, i'm
> > > investigating it recently, i take some test on Linux(Fedora) hvm guest,
> > it
> > > works good. (Xen-4.1.3 and Linux 3.5.0).
> > >
> > > The most confused question of me is why did Xen Console come to mind in
> > the
> > > early date, What's the requirement? Was it going to replace the emulated
> > > serial by qemu, or just an additional way to access the guest with high
> > > performance or sth other?
> > >
> > > I have post this in the xen-devel mail list and got some useful answer,
> >
> > Then lets add CC to it again.
> > > since you are the expert about it, I'd like to consult you for the
> > original
> > > answer, thanks.
> >
> > The answer is 'additional way to access the guest without having to emulate
> > the serial port'
> >
> > Thanks.
> 
> So this will improve the performance a lot on both Dom0 and DomU side,
> since the speed is not very critical when accessing a guest via console, I
> guess the most important benefit is to reduce the cpu cost of dom0  when
> emulating the serial port, is it or sth other?

Sure. But as you said - you don't use the console that often.
> 
> I have talked to stefano and he told the early printk is not supported by
> HVM guest while it's available for PV guest with "earlyprintk=xen"
> indicated in kernel boot up parameters, so is there any concern to support
> it in the future? or is this worth to do?

Correct. It could be supported, but it is more of a diagnostic tool (earlyprintk
that is it).
And as such you can also just use 'earlyprintk=serial' to help with that.

Re: Question about Xen Console

[Wei Xu]

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On Monday, April 1, 2013, Konrad Rzeszutek Wilk wrote:

> On Mon, Apr 01, 2013 at 09:16:04PM +0800, Wei Xu wrote:
> > On Mon, Apr 1, 2013 at 8:47 PM, Konrad Rzeszutek Wilk <
> > konrad.wilk@oracle.com <javascript:;>> wrote:
> >
> > > On Mon, Apr 01, 2013 at 01:59:15PM +0800, Wei Xu wrote:
> > > > Hi Konrad,
> > > > I'd like to consult you some questions about the Xen Console, i'm
> > > > investigating it recently, i take some test on Linux(Fedora) hvm
> guest,
> > > it
> > > > works good. (Xen-4.1.3 and Linux 3.5.0).
> > > >
> > > > The most confused question of me is why did Xen Console come to mind
> in
> > > the
> > > > early date, What's the requirement? Was it going to replace the
> emulated
> > > > serial by qemu, or just an additional way to access the guest with
> high
> > > > performance or sth other?
> > > >
> > > > I have post this in the xen-devel mail list and got some useful
> answer,
> > >
> > > Then lets add CC to it again.
> > > > since you are the expert about it, I'd like to consult you for the
> > > original
> > > > answer, thanks.
> > >
> > > The answer is 'additional way to access the guest without having to
> emulate
> > > the serial port'
> > >
> > > Thanks.
> >
> > So this will improve the performance a lot on both Dom0 and DomU side,
> > since the speed is not very critical when accessing a guest via console,
> I
> > guess the most important benefit is to reduce the cpu cost of dom0  when
> > emulating the serial port, is it or sth other?
>
> Sure. But as you said - you don't use the console that often.
> >
> > I have talked to stefano and he told the early printk is not supported by
> > HVM guest while it's available for PV guest with "earlyprintk=xen"
> > indicated in kernel boot up parameters, so is there any concern to
> support
> > it in the future? or is this worth to do?
>
> Correct. It could be supported, but it is more of a diagnostic tool
> (earlyprintk
> that is it).
> And as such you can also just use 'earlyprintk=serial' to help with that.
>

> Got it，thanks.

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