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Re: [PATCH RT] net: move xmit_recursion to per-task variable on -RT

From Hannes Frederic Sowa <hannes@stressinduktion.org>
Newsgroups linux.kernel
Subject Re: [PATCH RT] net: move xmit_recursion to per-task variable on -RT
Date 2016-01-14 23:10 +0100
Message-ID <qQYfF-533-21@gated-at.bofh.it> (permalink)
References <qQvx1-1Cf-19@gated-at.bofh.it> <qQxyP-300-55@gated-at.bofh.it> <qQRxx-8vf-29@gated-at.bofh.it>
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On 14.01.2016 15:50, Sebastian Andrzej Siewior wrote:
> * Thomas Gleixner | 2016-01-13 18:31:46 [+0100]:
>
>> On Wed, 13 Jan 2016, Sebastian Andrzej Siewior wrote:
>>> +#ifdef CONFIG_PREEMPT_RT_FULL
>>> +static inline int dev_recursion_level(void)
>>> +{
>>> +	return atomic_read(&current->xmit_recursion);
>>
>> Why would you need an atomic here. current does hardly race against itself.
>
> right.

We are just adding a second recursion limit solely to openvswitch which 
has the same problem:

https://patchwork.ozlabs.org/patch/566769/

This time also we depend on rcu_read_lock marking the section being 
nonpreemptible. Nice would be a more generic solution here which doesn't 
need to always add something to *current.

Thanks,
Hannes

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[PATCH RT] net: move xmit_recursion to per-task variable on -RT Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2016-01-13 16:30 +0100
  Re: [PATCH RT] net: move xmit_recursion to per-task variable on  -RT Thomas Gleixner <tglx@linutronix.de> - 2016-01-13 18:40 +0100
    Re: [PATCH RT] net: move xmit_recursion to per-task variable on -RT Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2016-01-14 16:00 +0100
      Re: [PATCH RT] net: move xmit_recursion to per-task variable on -RT Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-01-14 23:10 +0100
        Re: [PATCH RT] net: move xmit_recursion to per-task variable on -RT Eric Dumazet <eric.dumazet@gmail.com> - 2016-01-14 23:30 +0100
          Re: [PATCH RT] net: move xmit_recursion to per-task variable on -RT Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-01-15 00:10 +0100
            Re: [PATCH RT] net: move xmit_recursion to per-task variable on  -RT Thomas Gleixner <tglx@linutronix.de> - 2016-01-15 09:30 +0100
              Re: [PATCH RT] net: move xmit_recursion to per-task variable on -RT Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-01-15 10:40 +0100

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