Xen devel - Nov 2010 - Local APIC doesn''t implement "One shot" mode?

I''ve now have gotten our OS running on Xen 4.0.  Many thanks.

However it appears that the Local APIC presented to the client only 
implements the "periodic" timer mode, and not "one shot"
(bit 17 of the
APIC Local Vector Table).  I say "apparently" because I have limited
time
on the hardware so I didn''t have time to write a definitive test case,
but
the external visible behavior is that the local apic timer does not stop 
at zero when programmed for "one-shot" mode.  This isn''t
overly difficult
for me to work around, but I thought I''d mention it just in case it 
warranted fixing.  If desired, I can confirm my conjecture the next time I 
have time on the hardware.

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On 23/11/2010 14:00, "alarson@ddci.com" <alarson@ddci.com>
wrote:
> I''ve now have gotten our OS running on Xen 4.0.  Many thanks.
> 
> However it appears that the Local APIC presented to the client only
> implements the "periodic" timer mode, and not "one
shot" (bit 17 of the
> APIC Local Vector Table).  I say "apparently" because I have
limited time
> on the hardware so I didn''t have time to write a definitive test
case, but
> the external visible behavior is that the local apic timer does not stop
> at zero when programmed for "one-shot" mode.  This isn''t
overly difficult
> for me to work around, but I thought I''d mention it just in case
it
> warranted fixing.  If desired, I can confirm my conjecture the next time I
> have time on the hardware.
You are correct in your observation. If you care about correct one-shot
behaviour for reads of the current-count register, I can propose a patch for
you to test?

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


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xen-devel-bounces@lists.xensource.com wrote on 11/23/2010 08:05:33 AM:

AL> On 23/11/2010 14:00, "alarson@ddci.com"
<alarson@ddci.com> wrote:

AL> However it appears that the Local APIC presented to the client
AL> only implements the "periodic" timer mode, and not "one
shot" (bit
AL> 17 of the APIC Local Vector Table).  ...

KF> You are correct in your observation. If you care about correct
KF> one-shot behaviour for reads of the current-count register, I can
KF> propose a patch for you to test?

Certainly.  I may not get a chance to test it until next week though,
depending on HW scheduling.

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Please try the attached patch.

 K.

On 23/11/2010 14:00, "alarson@ddci.com" <alarson@ddci.com>
wrote:
> I''ve now have gotten our OS running on Xen 4.0.  Many thanks.
> 
> However it appears that the Local APIC presented to the client only
> implements the "periodic" timer mode, and not "one
shot" (bit 17 of the
> APIC Local Vector Table).  I say "apparently" because I have
limited time
> on the hardware so I didn''t have time to write a definitive test
case, but
> the external visible behavior is that the local apic timer does not stop
> at zero when programmed for "one-shot" mode.  This isn''t
overly difficult
> for me to work around, but I thought I''d mention it just in case
it
> warranted fixing.  If desired, I can confirm my conjecture the next time I
> have time on the hardware.
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel


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