Re: Unhandled IRQs on AMD E-450
From: Josh Boyer
Date: Fri Apr 27 2012 - 09:49:13 EST
On Fri, Apr 27, 2012 at 9:28 AM, Jeroen Van den Keybus
<jeroen.vandenkeybus@xxxxxxxxx> wrote:
>> Apparently there are
>> some pieces of hardware that generate a small number of spurious IRQs
>> "normally" and lowering the threshold to such a small value caused
>> those machines to kick into polling mode when they really didn't need
>> to.
>
> Hm. I'd really expect a spurious IRQ to happen as its name suggests:
> spuriously. What kind of hardware behaves like this ?
I'd have to go back and look through all the bug reports. Essentially,
it wound up being "this used to work fine, now I get stuck in polling
mode". When we dropped the patch in those cases, it went back to
working fine.
I'm not sure if it was a matter of a shared IRQ hitting quickly in
succession, or if it was really small bursts of spurious IRQs.
>> 1) While the quirk helps shield people without the buggy bridge, it
>> doesn't help the case where people have the bridge, but they have no
>> devices actually behind it. That means such setups hit the polling
>> mode when they don't really need to as described above.
>
> Curious, the polling mode is left until a new spurious IRQ is detected.
Yes, except the threshold was lowered from 100000 to 10 in the original
patch. Apparently that's too low.
>> 2) People, rightfully, complain that it makes inter-activity on their
>> desktop pretty laggy. The mouse pointer jumps around a lot and key
>> strokes are often missed. For a server class machine, I doubt it
>> would matter much but Fedora is essentially a desktop distro so that
>> tends to be a high priority.
>
> Again, I am a bit surprised. However, according to your patch:
>
>> + if (!irq_poll_and_retry)
>> + if (likely(desc->irq_count < 100000))
>> + return;
>> + else
>> + if (likely(desc->irq_count < 10))
>> + return;
>
> Don't you mean :
>
> + if (!irq_poll_and_retry) {
> + if (likely(desc->irq_count < 100000))
> + return;
> + }
> + else {
> + if (likely(desc->irq_count < 10))
> + return;
> + }
Indeed. Probably do.
josh
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