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From: roszenrami@gmail.com (Rami Rosen)
To: kernelnewbies@lists.kernelnewbies.org
Subject: When to use threaded interrupts?
Date: Sun, 13 Sep 2015 14:16:48 +0300	[thread overview]
Message-ID: <CAKoUArm84FQMShz4JvdRudMaccykfsb-vLZ6HO2C_WkW=t+AKw@mail.gmail.com> (raw)
In-Reply-To: <CADxo8W+znemZQypHR8d77NozyKwe52P9OMFDk=ALZiNdf3Jemw@mail.gmail.com>

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@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@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@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
>> >
>
>

  reply	other threads:[~2015-09-13 11:16 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-09-10 17:49 When to use threaded interrupts? Kosta Zertsekel
2015-09-10 20:09 ` Rami Rosen
2015-09-13  6:24   ` Kosta Zertsekel
2015-09-13 11:16     ` Rami Rosen [this message]
2015-09-15 18:02       ` Kosta Zertsekel
2015-09-15 19:05         ` Greg KH

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