Re: [PATCH 1/3] make migrate disable/enable conditioned on softirq_nestcnt transition

2013-12-15 Thread Sebastian Andrzej Siewior
* Steven Rostedt | 2013-12-05 19:45:30 [-0500]:

>On Fri, 6 Dec 2013 00:42:22 +0100
>Nicholas Mc Guire  wrote:
>> --- a/kernel/softirq.c
>> +++ b/kernel/softirq.c
>> @@ -569,8 +569,8 @@ static void do_current_softirqs(int need_rcu_bh_qs)
>>  
>>  void local_bh_disable(void)
>>  {
>> -migrate_disable();
>> -current->softirq_nestcnt++;
>> +if (++current->softirq_nestcnt == 1)
>> +migrate_disable();
>>  }
>>  EXPORT_SYMBOL(local_bh_disable);
>>  
>> @@ -584,8 +584,8 @@ void local_bh_enable(void)
>>  do_current_softirqs(1);
>>  local_irq_enable();
>>  
>> -current->softirq_nestcnt--;
>> -migrate_enable();
>> +if (--current->softirq_nestcnt == 0)
>> +migrate_enable();
>
>I wonder if we should add a:
>
>   BUG_ON(current->softirq_nestcnt < 0);

We have a WARN_ON() in each enable path. That one in local_bh_enable()
isn't part of the context here. If you want to s/WARN_/BUG_/ then I
would prefer not to since there are a few people with no UART and this
could break the system while the current sollution keeps the system
running.

>As for the patch, I haven't found anything wrong with it.
>
>Reviewed-by: Steven Rostedt 
Thanks.

Sebastian
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Re: [PATCH 1/3] make migrate disable/enable conditioned on softirq_nestcnt transition

2013-12-15 Thread Sebastian Andrzej Siewior
* Steven Rostedt | 2013-12-05 19:45:30 [-0500]:

On Fri, 6 Dec 2013 00:42:22 +0100
Nicholas Mc Guire der.h...@hofr.at wrote:
 --- a/kernel/softirq.c
 +++ b/kernel/softirq.c
 @@ -569,8 +569,8 @@ static void do_current_softirqs(int need_rcu_bh_qs)
  
  void local_bh_disable(void)
  {
 -migrate_disable();
 -current-softirq_nestcnt++;
 +if (++current-softirq_nestcnt == 1)
 +migrate_disable();
  }
  EXPORT_SYMBOL(local_bh_disable);
  
 @@ -584,8 +584,8 @@ void local_bh_enable(void)
  do_current_softirqs(1);
  local_irq_enable();
  
 -current-softirq_nestcnt--;
 -migrate_enable();
 +if (--current-softirq_nestcnt == 0)
 +migrate_enable();

I wonder if we should add a:

   BUG_ON(current-softirq_nestcnt  0);

We have a WARN_ON() in each enable path. That one in local_bh_enable()
isn't part of the context here. If you want to s/WARN_/BUG_/ then I
would prefer not to since there are a few people with no UART and this
could break the system while the current sollution keeps the system
running.

As for the patch, I haven't found anything wrong with it.

Reviewed-by: Steven Rostedt rost...@goodmis.org
Thanks.

Sebastian
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Re: [PATCH 1/3] make migrate disable/enable conditioned on softirq_nestcnt transition

2013-12-05 Thread Steven Rostedt
BTW, Please Cc LKML when sending patches. It is the kernel you are
modifying, not userspace.

On Fri, 6 Dec 2013 00:42:22 +0100
Nicholas Mc Guire  wrote:

> 
>  This patch removes the recursive calls to migrate_disable/enable in 
>  local_bh_disable/enable
> 
>  the softirq-local-lock.patch introduces local_bh_disable/enable wich 
>  decrements/increments the current->softirq_nestcnt and disable/enables
>  migration as well. as softirq_nestcnt (include/linux/sched.h conditioned
>  on CONFIG_PREEMPT_RT_BASE) already is tracking the nesting level of the
>  recursive calls to local_bh_disable/enable (all in kernel/softirq.c) - no 
>  need to do it twice.
> 
>  migrate_disable/enable thus can be conditionsed on softirq_nestcnt making
>  a transition from 0-1 to disable migration and 1-0 to re-enable it.
> 
>  patch on top of 3.12.1-rt4
> 
>  No change of functional behavior, this does noticably reduce the observed 
>  nesting level of migrate_disable/enable 
> 
> Signed-off-by: Nicholas Mc Guire 
> ---
>  kernel/softirq.c |   14 --
>  1 files changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index 9a7268f..16ebbd9 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -569,8 +569,8 @@ static void do_current_softirqs(int need_rcu_bh_qs)
>  
>  void local_bh_disable(void)
>  {
> - migrate_disable();
> - current->softirq_nestcnt++;
> + if (++current->softirq_nestcnt == 1)
> + migrate_disable();
>  }
>  EXPORT_SYMBOL(local_bh_disable);
>  
> @@ -584,8 +584,8 @@ void local_bh_enable(void)
>   do_current_softirqs(1);
>   local_irq_enable();
>  
> - current->softirq_nestcnt--;
> - migrate_enable();
> + if (--current->softirq_nestcnt == 0)
> + migrate_enable();

I wonder if we should add a:

BUG_ON(current->softirq_nestcnt < 0);

As for the patch, I haven't found anything wrong with it.

Reviewed-by: Steven Rostedt 

-- Steve

>  }
>  EXPORT_SYMBOL(local_bh_enable);
>  
> @@ -597,8 +597,10 @@ EXPORT_SYMBOL(local_bh_enable_ip);
>  
>  void _local_bh_enable(void)
>  {
> - current->softirq_nestcnt--;
> - migrate_enable();
> + if (WARN_ON(current->softirq_nestcnt == 0))
> + return;
> + if (--current->softirq_nestcnt == 0)
> + migrate_enable();
>  }
>  EXPORT_SYMBOL(_local_bh_enable);
>  

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Re: [PATCH 1/3] make migrate disable/enable conditioned on softirq_nestcnt transition

2013-12-05 Thread Steven Rostedt
BTW, Please Cc LKML when sending patches. It is the kernel you are
modifying, not userspace.

On Fri, 6 Dec 2013 00:42:22 +0100
Nicholas Mc Guire der.h...@hofr.at wrote:

 
  This patch removes the recursive calls to migrate_disable/enable in 
  local_bh_disable/enable
 
  the softirq-local-lock.patch introduces local_bh_disable/enable wich 
  decrements/increments the current-softirq_nestcnt and disable/enables
  migration as well. as softirq_nestcnt (include/linux/sched.h conditioned
  on CONFIG_PREEMPT_RT_BASE) already is tracking the nesting level of the
  recursive calls to local_bh_disable/enable (all in kernel/softirq.c) - no 
  need to do it twice.
 
  migrate_disable/enable thus can be conditionsed on softirq_nestcnt making
  a transition from 0-1 to disable migration and 1-0 to re-enable it.
 
  patch on top of 3.12.1-rt4
 
  No change of functional behavior, this does noticably reduce the observed 
  nesting level of migrate_disable/enable 
 
 Signed-off-by: Nicholas Mc Guire der.h...@hofr.at
 ---
  kernel/softirq.c |   14 --
  1 files changed, 8 insertions(+), 6 deletions(-)
 
 diff --git a/kernel/softirq.c b/kernel/softirq.c
 index 9a7268f..16ebbd9 100644
 --- a/kernel/softirq.c
 +++ b/kernel/softirq.c
 @@ -569,8 +569,8 @@ static void do_current_softirqs(int need_rcu_bh_qs)
  
  void local_bh_disable(void)
  {
 - migrate_disable();
 - current-softirq_nestcnt++;
 + if (++current-softirq_nestcnt == 1)
 + migrate_disable();
  }
  EXPORT_SYMBOL(local_bh_disable);
  
 @@ -584,8 +584,8 @@ void local_bh_enable(void)
   do_current_softirqs(1);
   local_irq_enable();
  
 - current-softirq_nestcnt--;
 - migrate_enable();
 + if (--current-softirq_nestcnt == 0)
 + migrate_enable();

I wonder if we should add a:

BUG_ON(current-softirq_nestcnt  0);

As for the patch, I haven't found anything wrong with it.

Reviewed-by: Steven Rostedt rost...@goodmis.org

-- Steve

  }
  EXPORT_SYMBOL(local_bh_enable);
  
 @@ -597,8 +597,10 @@ EXPORT_SYMBOL(local_bh_enable_ip);
  
  void _local_bh_enable(void)
  {
 - current-softirq_nestcnt--;
 - migrate_enable();
 + if (WARN_ON(current-softirq_nestcnt == 0))
 + return;
 + if (--current-softirq_nestcnt == 0)
 + migrate_enable();
  }
  EXPORT_SYMBOL(_local_bh_enable);
  

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