replacement of tasklet_hrtimer_init in RT

replacement of tasklet_hrtimer_init in RT

[Chris Caudle]

I recently began helping someone test a new multimedia driver (network
audio) and found that the driver would not compile on my machine running
an RT kernel because the driver used tasklet_hrtimer_init(), but that
function is not defined in interrupt.h in the RT  patched kernel.

What should be used in place of that, and where should be look for
documentation describing any differences that need to be accomodated?

-- 
Chris Caudle

Re: replacement of tasklet_hrtimer_init in RT

[Henrik Austad]

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Hi Chris,

On Tue, Oct 24, 2017 at 11:33:46AM -0500, Chris Caudle wrote:
> I recently began helping someone test a new multimedia driver (network
> audio) and found that the driver would not compile on my machine running
> an RT kernel because the driver used tasklet_hrtimer_init(), but that
> function is not defined in interrupt.h in the RT  patched kernel.

/me eyes include/linux/interupt.h and kernel/softirq.c and finds 
tasklet_hrtimer_init().

It is marked EXPORT_SYMBOL_GPL() though, so if you do not export the 
modules as GPL, it won't resolve that symbol.

If this is not the case, please provide which kernel-version and PREEMPT-RT 
patch version you are using. A .config would probably also be helpful.

> What should be used in place of that, and where should be look for
> documentation describing any differences that need to be accomodated?

Using tasklets is somewhat frowned upon -have you tried using a 
kernelthread instead? (You can adjust priority and set affinity for 
threads)

-Henrik

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Re: replacement of tasklet_hrtimer_init in RT

[Chris Caudle]

On Wed, October 25, 2017 12:34 am, Henrik Austad wrote:
> /me eyes include/linux/interupt.h and kernel/softirq.c and finds
> tasklet_hrtimer_init().

Are you sure?  I previously sent a copy of my interrupt.h to the list, may
have been rejected because I attached the file rather than copied inline.

I downloaded the patches file for 4.11.12-rt14 and searching for
tasklet_hrtimer_init() I find this reference:

0022-softirq-Remove-tasklet_hrtimer.patch:-tasklet_hrtimer_init(struct
tasklet_hrtimer *ttimer,

The very top lines of that 0022 patch file are these:

---------
From: Thomas Gleixner <tglx@linutronix.de>
Date: Thu, 31 Aug 2017 11:03:11 +0000
Subject: [PATCH 22/25] softirq: Remove tasklet_hrtimer

There are no more tasklet_hrtimer users of this interface.
Remove it.
---------

It looks to me like the tasklet_hrtimer interface is being intentionally
removed.

-- 
Chris Caudle

Re: replacement of tasklet_hrtimer_init in RT

[Chris Caudle]

On Wed, October 25, 2017 11:50 am, Chris Caudle wrote:
> I downloaded the patches file for 4.11.12-rt14 and searching for
> tasklet_hrtimer_init() I find this reference:
>
> 0022-softirq-Remove-tasklet_hrtimer.patch:-tasklet_hrtimer_init(struct
> tasklet_hrtimer *ttimer,
>
> The very top lines of that 0022 patch file are these:
>
> ---------
> From: Thomas Gleixner <tglx@linutronix.de>
> Date: Thu, 31 Aug 2017 11:03:11 +0000
> Subject: [PATCH 22/25] softirq: Remove tasklet_hrtimer
>
> There are no more tasklet_hrtimer users of this interface.
> Remove it.

Does anyone on this list know whether the tasklet_hrtimer interface will
be deprecated for mainline kernel as well?

Can anyone suggest a document that describes (hopefully simply enough for
a kernel beginner to understand) how to convert an existing implementation
from tasklet_hrtimer to an alternative?

thank you,
Chris Caudle

Re: replacement of tasklet_hrtimer_init in RT

[Henrik Austad]

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On Wed, Oct 25, 2017 at 11:50:01AM -0500, Chris Caudle wrote:
> On Wed, October 25, 2017 12:34 am, Henrik Austad wrote:
> > /me eyes include/linux/interupt.h and kernel/softirq.c and finds
> > tasklet_hrtimer_init().
> 
> Are you sure?  I previously sent a copy of my interrupt.h to the list, may
> have been rejected because I attached the file rather than copied inline.

do'h! you're right, I was looking in the wrong version (for some reason I 
was looking at v4.9.33-rt23) - it has since been removed.

> I downloaded the patches file for 4.11.12-rt14 and searching for
> tasklet_hrtimer_init() I find this reference:
> 
> 0022-softirq-Remove-tasklet_hrtimer.patch:-tasklet_hrtimer_init(struct
> tasklet_hrtimer *ttimer,
> 
> The very top lines of that 0022 patch file are these:

yeah, I see it, my bad, sorry

-Henrik

> ---------
> From: Thomas Gleixner <tglx@linutronix.de>
> Date: Thu, 31 Aug 2017 11:03:11 +0000
> Subject: [PATCH 22/25] softirq: Remove tasklet_hrtimer
> 
> There are no more tasklet_hrtimer users of this interface.
> Remove it.
> ---------
> 
> It looks to me like the tasklet_hrtimer interface is being intentionally
> removed.
> 
> -- 
> Chris Caudle
> 
> 

-- 
Henrik Austad

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Re: replacement of tasklet_hrtimer_init in RT

[Sebastian Andrzej Siewior]

On 2017-10-24 11:33:46 [-0500], Chris Caudle wrote:
> I recently began helping someone test a new multimedia driver (network
> audio) and found that the driver would not compile on my machine running
> an RT kernel because the driver used tasklet_hrtimer_init(), but that
> function is not defined in interrupt.h in the RT  patched kernel.
> 
> What should be used in place of that, and where should be look for
> documentation describing any differences that need to be accomodated?

So what you want to do in -RT right now is to use something like the
mac80211_hwsim.c:
	https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/commit/?h=linux-4.13.y-rt&id=29158ad20a5363c581110497f430fa98b4280c5c
	
but I will update that softirq patch I have now in tree with the
version which is staged for upstream and then it will change slightly:
	https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=WIP.timers&id=77d37439a5b64036c1c168752a95e80f6ebe241a

Sebastian