linux-kernel - Re: Question regarding RT patches for ARM

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Date:   Mon, 15 May 2017 16:07:47 +0200
From:   Fawad Lateef <fawadlateef@...il.com>
To:     Sebastian Andrzej Siewior <sebastian.siewior@...utronix.de>
Cc:     GuJiangfei <qiledexin@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kernelnewbies <kernelnewbies@...nelnewbies.org>,
        linux-rt-users@...r.kernel.org
Subject: Re: Question regarding RT patches for ARM

Hi Sebastian,


On 15 May 2017 at 15:47, Sebastian Andrzej Siewior
<sebastian.siewior@...utronix.de> wrote:
> On 2017-05-15 15:09:45 [+0200], Fawad Lateef wrote:
>> Hi,
>>
>> I am talking in general about RT patches. Like downloaded 4.9.20 from
>> kernel.org and applied patch "4.9.20-rt16.patch".
>
> understood
>
>> On 15 May 2017 at 14:51, GuJiangfei <qiledexin@....com> wrote:
>> > Which rt patch do you mean?
>> >
>> >
>> > 发自网易邮箱大师
>> > On 05/15/2017 20:44, Fawad Lateef wrote:
>> >
>> > Hi All,
>> >
>> > I am working on custom i.MX6 quad hardware and using RT patches for
>> > almost latest stable kernel 4.9 and facing some weird system stall OR
>> > 'unhandled page fault - exceptions'.
>
> and you are sure that this problems are caused by the RT patch or is
> there a chance that this is unrelated to the RT patch?
>

The hardware platform is used by many other projects/products _but_
none of them is using RT patches.
So really not sure if its hardware issue, though problem can be seen
only in RT version of kernel which is needed for project.

>> > Just want to confirm that "are RT patches for ARM are stable OR they
>> > are still experimental?" As I heard from my other colleagues that RT
>> > patches are not stable for ARM and should be avoided.
>
> It is stable and I am not aware of any ARM / IMX specific problems.
>

Ok, thanks. Good to know. I actually want this sort of confirmation as
till now "platform/hardware manufacturer" says RT is unstable and
should not be used (as newer kernel already have low-latency)

> Since this got here from kernelnewbies: I would not recommend the
> Preempt-RT patch set to add to any kernel just to have fancy patches.
> People use it because they need to fulfill specific requirements which
> would not work without it. You might want to check some of the
> documentation in the RT-wiki
>         https://wiki.linuxfoundation.org/realtime/documentation/start
>

In our case we need RT because few other hardware components (external
devices) needs really strict hard-limit and we can't miss that.

(BTW I should have not included kernelnewbies in the CC list, but as
was asking question in general that's why included).

>> > Thanks in advance,
>> >
>> > -- Fawad Lateef
>
> Sebastian

Thanks,

Fawad Lateef