Priorities of IRQ handlers

Priorities of IRQ handlers

[John Sigler]

Hello everyone,

I'm running 2.6.22.1-rt9 on x86.

CONFIG_PREEMPT_RT=y
CONFIG_PREEMPT=y
CONFIG_PREEMPT_SOFTIRQS=y
CONFIG_PREEMPT_HARDIRQS=y
CONFIG_PREEMPT_BKL=y
# CONFIG_CLASSIC_RCU is not set
CONFIG_PREEMPT_RCU=y

I need to change the priorities of several soft and hard IRQ handlers.

Namely,

o reduce the prio of "softirq-timer" handler to 10

o reduce the prio of IRQ14 and IRQ15 handlers to 20
   (my flash drives do not support DMA BTW...)

o boost the prio of my I/O boards' IRQ handlers to 60
   (there can be 1 or 2 boards, the driver is a kernel module
    which is loaded after the system has booted.)

I've written a short program that calls
   sched_setscheduler(pid, SCHED_FIFO, &param);
with the appropriate pid, which I look up using ps -ef

I need to automate the process of tweaking priorities.

Can someone offer advice and / or pointers?

Regards.

Re: Priorities of IRQ handlers

[Steven Rostedt]

On Mon, 26 Nov 2007, John Sigler wrote:

> I need to change the priorities of several soft and hard IRQ handlers.
>
> Namely,
>
> o reduce the prio of "softirq-timer" handler to 10
>
> o reduce the prio of IRQ14 and IRQ15 handlers to 20
>    (my flash drives do not support DMA BTW...)
>
> o boost the prio of my I/O boards' IRQ handlers to 60
>    (there can be 1 or 2 boards, the driver is a kernel module
>     which is loaded after the system has booted.)
>
> I've written a short program that calls
>    sched_setscheduler(pid, SCHED_FIFO, &param);
> with the appropriate pid, which I look up using ps -ef

Look for the program "chrt". It does this for you. This program is
avaliable in all major distrobutions of Linux.

>
> I need to automate the process of tweaking priorities.
>
> Can someone offer advice and / or pointers?

Perhaps look at one of the Start up scripts, and add the chrt command
there.

-- Steve

Re: Priorities of IRQ handlers

[John Sigler]

Hello Steven,

Steven Rostedt wrote:

> John Sigler wrote:
> 
>> I need to change the priorities of several soft and hard IRQ handlers.
>>
>> Namely,
>>
>> o reduce the prio of "softirq-timer" handler to 10
>>
>> o reduce the prio of IRQ14 and IRQ15 handlers to 20
>>    (my flash drives do not support DMA BTW...)
>>
>> o boost the prio of my I/O boards' IRQ handlers to 60
>>    (there can be 1 or 2 boards, the driver is a kernel module
>>     which is loaded after the system has booted.)
>>
>> I've written a short program that calls
>>    sched_setscheduler(pid, SCHED_FIFO, &param);
>> with the appropriate pid, which I look up using ps -ef
> 
> Look for the program "chrt". It does this for you. This program is
> available in all major distributions of Linux.

Thanks for the tip.

For the record, I found schedutils on Robert Love's page:

http://rlove.org/
http://rlove.org/misc/schedutils-1.5.0.tar.gz

However, I had already solved that part of the problem with a
program of my own.

My real problem is: the IRQ handlers for the I/O boards are
only instantiated when the kernel module is inserted. How do
I /reliably/ determine their pid?

e.g. on one system, the IRQ handler for my I/O board is IRQ5
with pid 745. On another system, it's IRQ20 with pid 808.
On a third system they're IRQ20 and IRQ21 with pid 239 and 240.

The only solution I see is to examine /proc/interrupts to find the
IRQ handler(s) then ps to lookup their pid, but that feels like a
dirty hack.

These interrupt handlers are all spawned by kthreadd. I thought
there would be some way to ask kthreadd to tweak the priorities.

>> I need to automate the process of tweaking priorities.
>>
>> Can someone offer advice and / or pointers?
> 
> Perhaps look at one of the startup scripts, and add the chrt
> command there.

Which startup scripts?

Regards.

Re: Priorities of IRQ handlers

[K.R. Foley]

John Sigler wrote:
> Hello Steven,
> 
> Steven Rostedt wrote:
> 
>> John Sigler wrote:
>>
>>> I need to change the priorities of several soft and hard IRQ handlers.
>>>
>>> Namely,
>>>
>>> o reduce the prio of "softirq-timer" handler to 10
>>>
>>> o reduce the prio of IRQ14 and IRQ15 handlers to 20
>>>    (my flash drives do not support DMA BTW...)
>>>
>>> o boost the prio of my I/O boards' IRQ handlers to 60
>>>    (there can be 1 or 2 boards, the driver is a kernel module
>>>     which is loaded after the system has booted.)
>>>
>>> I've written a short program that calls
>>>    sched_setscheduler(pid, SCHED_FIFO, &param);
>>> with the appropriate pid, which I look up using ps -ef
>>
>> Look for the program "chrt". It does this for you. This program is
>> available in all major distributions of Linux.
> 
> Thanks for the tip.
> 
> For the record, I found schedutils on Robert Love's page:
> 
> http://rlove.org/
> http://rlove.org/misc/schedutils-1.5.0.tar.gz
> 
> However, I had already solved that part of the problem with a
> program of my own.
> 
> My real problem is: the IRQ handlers for the I/O boards are
> only instantiated when the kernel module is inserted. How do
> I /reliably/ determine their pid?

What about something like:
chrt -f -p 99 `/sbin/pidof 'IRQ 8'`

> 
> e.g. on one system, the IRQ handler for my I/O board is IRQ5
> with pid 745. On another system, it's IRQ20 with pid 808.
> On a third system they're IRQ20 and IRQ21 with pid 239 and 240.
> 
> The only solution I see is to examine /proc/interrupts to find the
> IRQ handler(s) then ps to lookup their pid, but that feels like a
> dirty hack.
> 
> These interrupt handlers are all spawned by kthreadd. I thought
> there would be some way to ask kthreadd to tweak the priorities.

I have created patches to do this in the past. However, because you are
setting different threads to different priorities it probably makes more
sense to do this from user space. Much more flexible.

> 
>>> I need to automate the process of tweaking priorities.
>>>
>>> Can someone offer advice and / or pointers?
>>
>> Perhaps look at one of the startup scripts, and add the chrt
>> command there.
> 
> Which startup scripts?
> 
> Regards.
> -
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> 


-- 
   kr

Re: Priorities of IRQ handlers

[Arnaldo Carvalho de Melo]

Em Wed, Nov 28, 2007 at 08:12:24AM -0600, K.R. Foley escreveu:
> John Sigler wrote:
> > Hello Steven,
> > 
> > Steven Rostedt wrote:
> > 
> >> John Sigler wrote:
> >>
> >>> I need to change the priorities of several soft and hard IRQ handlers.
> >>>
> >>> Namely,
> >>>
> >>> o reduce the prio of "softirq-timer" handler to 10
> >>>
> >>> o reduce the prio of IRQ14 and IRQ15 handlers to 20
> >>>    (my flash drives do not support DMA BTW...)
> >>>
> >>> o boost the prio of my I/O boards' IRQ handlers to 60
> >>>    (there can be 1 or 2 boards, the driver is a kernel module
> >>>     which is loaded after the system has booted.)
> >>>
> >>> I've written a short program that calls
> >>>    sched_setscheduler(pid, SCHED_FIFO, &param);
> >>> with the appropriate pid, which I look up using ps -ef
> >>
> >> Look for the program "chrt". It does this for you. This program is
> >> available in all major distributions of Linux.
> > 
> > Thanks for the tip.
> > 
> > For the record, I found schedutils on Robert Love's page:
> > 
> > http://rlove.org/
> > http://rlove.org/misc/schedutils-1.5.0.tar.gz
> > 
> > However, I had already solved that part of the problem with a
> > program of my own.
> > 
> > My real problem is: the IRQ handlers for the I/O boards are
> > only instantiated when the kernel module is inserted. How do
> > I /reliably/ determine their pid?
> 
> What about something like:
> chrt -f -p 99 `/sbin/pidof 'IRQ 8'`

If he knows that IRQ 8 is associated with his device, that is ok,
but how to map device -> IRQ in the first place?
 
> > 
> > e.g. on one system, the IRQ handler for my I/O board is IRQ5
> > with pid 745. On another system, it's IRQ20 with pid 808.
> > On a third system they're IRQ20 and IRQ21 with pid 239 and 240.

See?

Perhaps he could use a kernel command line where he would tell that
for the string used in request_irq the kthread priority should be N.

IIRC there was somebody trying to write a patch to support this at some
point in this list...

- Arnaldo

Re: Priorities of IRQ handlers

[Sven-Thorsten Dietrich]

On Wed, 2007-11-28 at 08:12 -0600, K.R. Foley wrote:
> John Sigler wrote:
> > Hello Steven,
> > 
> > Steven Rostedt wrote:
> > 
> >> John Sigler wrote:
> >>
> >>> I need to change the priorities of several soft and hard IRQ handlers.
> >>>
> >>> Namely,
> >>>
> >>> o reduce the prio of "softirq-timer" handler to 10
> >>>
> >>> o reduce the prio of IRQ14 and IRQ15 handlers to 20
> >>>    (my flash drives do not support DMA BTW...)
> >>>
> >>> o boost the prio of my I/O boards' IRQ handlers to 60
> >>>    (there can be 1 or 2 boards, the driver is a kernel module
> >>>     which is loaded after the system has booted.)
> >>>
> >>> I've written a short program that calls
> >>>    sched_setscheduler(pid, SCHED_FIFO, &param);
> >>> with the appropriate pid, which I look up using ps -ef
> >>
> >> Look for the program "chrt". It does this for you. This program is
> >> available in all major distributions of Linux.
> > 
> > Thanks for the tip.
> > 
> > For the record, I found schedutils on Robert Love's page:
> > 
> > http://rlove.org/
> > http://rlove.org/misc/schedutils-1.5.0.tar.gz
> > 
> > However, I had already solved that part of the problem with a
> > program of my own.
> > 
> > My real problem is: the IRQ handlers for the I/O boards are
> > only instantiated when the kernel module is inserted. How do
> > I /reliably/ determine their pid?
> 
> What about something like:
> chrt -f -p 99 `/sbin/pidof 'IRQ 8'`
> 
> > 

Keep in mind that if you are on a shared IRQ line, you will be boosting
the priority of other interrupts as well.

Sven

Re: Priorities of IRQ handlers

[Dominique Michel]

Le Wed, 28 Nov 2007 12:05:26 +0100,
John Sigler <linux.kernel@free.fr> a écrit :


> > Perhaps look at one of the startup scripts, and add the chrt
> > command there.
> 
> Which startup scripts?

You can look at the rtirq package: http://www.rncbc.org/jack/

Most of (all?) the multimedia linux distribution include it.

Cheers,
Dominique