default timer_mode in xen and in libxl

default timer_mode in xen and in libxl

[Stefano Stabellini]

Hi all,
I have just noticed that the timer mode default in libxl is not the
default in Xen.
The Xen default is HVMPTM_delay_for_missed_ticks, while libxl by
default sets it to LIBXL_TIMER_MODE_NO_DELAY_FOR_MISSED_TICKS that
obviously is HVMPTM_no_delay_for_missed_ticks.

Is there a reason for this?
If so, should we change the defalt in Xen too?

commit 2d058a444a1fa71ec47a673d08c2e74790ae67fb
Author: Ian Campbell <ian.campbell@citrix.com>
Date:   Thu Mar 1 12:26:13 2012 +0000

    libxl: use an explicit LIBXL_TIMER_MODE_DEFAULT value
    
    Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
    Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

Re: default timer_mode in xen and in libxl

[Keir Fraser]

On 25/04/2013 18:13, "Stefano Stabellini" <stefano.stabellini@eu.citrix.com>
wrote:

> Hi all,
> I have just noticed that the timer mode default in libxl is not the
> default in Xen.
> The Xen default is HVMPTM_delay_for_missed_ticks, while libxl by
> default sets it to LIBXL_TIMER_MODE_NO_DELAY_FOR_MISSED_TICKS that
> obviously is HVMPTM_no_delay_for_missed_ticks.
> 
> Is there a reason for this?
> If so, should we change the defalt in Xen too?

Default in Xen is the original mode before multiple modes were supported. We
kept that as default for old/other toolstacks, to avoid surprising change in
behaviour (e.g., when they restore old saved guests).

Default in libxl is the sane one for newly-created guests. Hardly any guests
care about or even want time to be delayed until timer interrupts are fired
off.

 -- Keir

> commit 2d058a444a1fa71ec47a673d08c2e74790ae67fb
> Author: Ian Campbell <ian.campbell@citrix.com>
> Date:   Thu Mar 1 12:26:13 2012 +0000
> 
>     libxl: use an explicit LIBXL_TIMER_MODE_DEFAULT value
>     
>     Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
>     Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel

Re: default timer_mode in xen and in libxl

[Ian Campbell]

On Thu, 2013-04-25 at 18:13 +0100, Stefano Stabellini wrote:
> Hi all,
> I have just noticed that the timer mode default in libxl is not the
> default in Xen.
> The Xen default is HVMPTM_delay_for_missed_ticks, while libxl by
> default sets it to LIBXL_TIMER_MODE_NO_DELAY_FOR_MISSED_TICKS that
> obviously is HVMPTM_no_delay_for_missed_ticks.
> 
> Is there a reason for this?
> If so, should we change the defalt in Xen too?
> 
> commit 2d058a444a1fa71ec47a673d08c2e74790ae67fb
> Author: Ian Campbell <ian.campbell@citrix.com>
> Date:   Thu Mar 1 12:26:13 2012 +0000
> 
>     libxl: use an explicit LIBXL_TIMER_MODE_DEFAULT value
>     
>     Signed-off-by: Ian Campbell <ian.campbell@citrix.com>

This commit just changed the way the default was set, but it didn't
change that default. Tracking back through the history it seems the
original change was:

        commit 85bd32d9085828dcfa29215c78d472afa0cfd3ad
        Author: Ian Jackson <Ian.Jackson@eu.citrix.com>
        Date:   Wed Jul 14 16:31:59 2010 +0100
        
            xl: default timer_mode to 1
            
            Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
        
        diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
        index e7aa89b..9706a6a 100644
        --- a/tools/libxl/xl_cmdimpl.c
        +++ b/tools/libxl/xl_cmdimpl.c
        @@ -205,7 +205,7 @@ static void init_build_info(libxl_domain_build_info *b_info, libxl_domain_create
                 b_info->u.hvm.viridian = 0;
                 b_info->u.hvm.hpet = 1;
                 b_info->u.hvm.vpt_align = 1;
        -        b_info->u.hvm.timer_mode = 0;
        +        b_info->u.hvm.timer_mode = 1;
             } else {
                 b_info->u.pv.slack_memkb = 8 * 1024;
             }
        
So you tell us ;-) (you see now why I'm picky about changelogs...)

Re: default timer_mode in xen and in libxl

[Stefano Stabellini]

On Fri, 26 Apr 2013, Ian Campbell wrote:
> On Thu, 2013-04-25 at 18:13 +0100, Stefano Stabellini wrote:
> > Hi all,
> > I have just noticed that the timer mode default in libxl is not the
> > default in Xen.
> > The Xen default is HVMPTM_delay_for_missed_ticks, while libxl by
> > default sets it to LIBXL_TIMER_MODE_NO_DELAY_FOR_MISSED_TICKS that
> > obviously is HVMPTM_no_delay_for_missed_ticks.
> > 
> > Is there a reason for this?
> > If so, should we change the defalt in Xen too?
> > 
> > commit 2d058a444a1fa71ec47a673d08c2e74790ae67fb
> > Author: Ian Campbell <ian.campbell@citrix.com>
> > Date:   Thu Mar 1 12:26:13 2012 +0000
> > 
> >     libxl: use an explicit LIBXL_TIMER_MODE_DEFAULT value
> >     
> >     Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> 
> This commit just changed the way the default was set, but it didn't
> change that default. Tracking back through the history it seems the
> original change was:
> 
>         commit 85bd32d9085828dcfa29215c78d472afa0cfd3ad
>         Author: Ian Jackson <Ian.Jackson@eu.citrix.com>
>         Date:   Wed Jul 14 16:31:59 2010 +0100
>         
>             xl: default timer_mode to 1
>             
>             Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
>         
>         diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
>         index e7aa89b..9706a6a 100644
>         --- a/tools/libxl/xl_cmdimpl.c
>         +++ b/tools/libxl/xl_cmdimpl.c
>         @@ -205,7 +205,7 @@ static void init_build_info(libxl_domain_build_info *b_info, libxl_domain_create
>                  b_info->u.hvm.viridian = 0;
>                  b_info->u.hvm.hpet = 1;
>                  b_info->u.hvm.vpt_align = 1;
>         -        b_info->u.hvm.timer_mode = 0;
>         +        b_info->u.hvm.timer_mode = 1;
>              } else {
>                  b_info->u.pv.slack_memkb = 8 * 1024;
>              }
>         
> So you tell us ;-) (you see now why I'm picky about changelogs...)

LOL
It must have been to match the default in xend.