When to use threaded interrupts?

[Rami Rosen]

Kosta,

This kernel and older ones include device drivers which use threaded IRQs
(call request_threaded_irq(), etc).
 For example, many of the driver under drivers/input/touchscreen are
using threaded IRQs:
Following link is from kernel 3.18:
http://lxr.free-electrons.com/source/drivers/input/touchscreen/ucb1400_ts.c?v=3.18

How did you came to the conclusion that this kernel does not support
threaded IRQs ? could it be that you simply do not use device drivers
that
use this mechanism ?

Regards,
Rami Rosen
http://ramirose.wix.com/ramirosen




On 13 September 2015 at 09:24, Kosta Zertsekel <zertsekel at gmail.com> wrote:
>>> I think I get the pro of using threaded interrupts - to decrease the
>>> maximum
>>> interrupt latency on RT workloads and/or RT machines (servers, embedded,
>>> etc.).
>>> So, I'd like to ask:
>>>    - Why not **all** of the drivers use the threaded interrupts?
>>>    - What are the cons of the threaded interrupts?
>>>
>> Just a wild assumption: maybe the cost of incurring context switches ?
>> (comparing to tasklets)
>
> I get that threaded IRQ is better than softIrqs because threaded IRQ
> supports
> priorities. On the other hand, added context switches surely get system
> slower.
> But from the practical point of view - why on relatively new Intel PC there
> are
> no threaded irqs at all?
>
> ```
> $ uname -a
> Linux kostaz-OptiPlex-7010 3.19.0-26-generic #28-Ubuntu SMP Tue Aug 11
> 14:16:32 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
> ```
>
> --- KostaZ
>
> On Thu, Sep 10, 2015 at 11:09 PM, Rami Rosen <roszenrami at gmail.com> wrote:
>>
>> Kosta,
>>
>> Just a wild assumption: maybe the cost of incurring context switches ?
>> (comparing to tasklets)
>>
>> Best Regards,
>> Rami Rosen
>> http://ramirose.wix.com/ramirosen
>>
>>
>>
>> On 10 September 2015 at 20:49, Kosta Zertsekel <zertsekel at gmail.com>
>> wrote:
>> > Hi guys,
>> >
>> > I hope I'm on right mailing list. :-)
>> > I think I get the pro of using threaded interrupts - to decrease the
>> > maximum
>> > interrupt latency on RT workloads and/or RT machines (servers, embedded,
>> > etc.).
>> >
>> > Also, I see that in 4.2 there are only ~76 drivers that use threaded
>> > interrupt:
>> > ```
>> > $ git grep -l IRQ_WAKE_THREAD | sort | grep -v "\.h" | wc -l
>> > 76
>> > ```
>> >
>> > So, I'd like to ask:
>> >    - Why not **all** of the drivers use the threaded interrupts?
>> >    - What are the cons of the threaded interrupts?
>> >
>> > Thanks,
>> > --- KostaZ
>> >
>> > _______________________________________________
>> > Kernelnewbies mailing list
>> > Kernelnewbies at kernelnewbies.org
>> > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>> >
>
>