Prev: [PATCH 1/6] NOMMU: Fix SYSV SHM for NOMMU
Next: trouble compiling dwalker's for-next tree
From: H. Peter Anvin on 13 Jan 2010 16:00
On 01/13/2010 12:36 PM, Eric W. Biederman wrote:
> "H. Peter Anvin" <hpa(a)zytor.com> writes:
>
>> On 01/11/2010 05:52 PM, Eric W. Biederman wrote:
>>>
>>> After having the documentation quoted at me. I am having a distinct
>>> memory of one piece of documentation saying:
>>> "interrupts within a priority level can be delivered in any order"
>>>
>>> So I am guessing there is not any ordering of interrupts in the same
>>> priority level until they get to the local apic.
>>>
>>
>> There is no ordering of interrupts before they hit the local APIC, since
>> the local APIC is what would serialize them...
>
> The io apic serializes them, and sends them over either the 2-wire
> bus or the front side bus. How much serialization and prioritization
> happens at that point I am not certain, but some certainly happens
> before you get to the local apic.
>

From the looks of the original 82093AA spec, the 2-wire bus did
round-robin between different APICs (including IOAPICs), and the IOAPIC
had no ordering guarantees whatsoever.

-hpa

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
From: H. Peter Anvin on 13 Jan 2010 16:10
On 01/13/2010 12:36 PM, Eric W. Biederman wrote:
> "H. Peter Anvin" <hpa(a)zytor.com> writes:
>
>> On 01/11/2010 05:52 PM, Eric W. Biederman wrote:
>>>
>>> After having the documentation quoted at me. I am having a distinct
>>> memory of one piece of documentation saying:
>>> "interrupts within a priority level can be delivered in any order"
>>>
>>> So I am guessing there is not any ordering of interrupts in the same
>>> priority level until they get to the local apic.
>>>
>>
>> There is no ordering of interrupts before they hit the local APIC, since
>> the local APIC is what would serialize them...
>
> The io apic serializes them, and sends them over either the 2-wire
> bus or the front side bus. How much serialization and prioritization
> happens at that point I am not certain, but some certainly happens
> before you get to the local apic.
>

Specifically, from the 82093AA spec:

"The interrupt number or the vector does not imply a particular priority
for being sent. The IOAPIC continually polls the 24 interrupts in a
rotating fashion, one at a time. The pending interrupt polled first is
the one sent."

In other words, the prioritization is all done at the LAPIC.

-hpa

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
First  |  Prev  | 
Pages: 1 2 3
Prev: [PATCH 1/6] NOMMU: Fix SYSV SHM for NOMMU
Next: trouble compiling dwalker's for-next tree