Re: [PATCH 1/4] sched: Add CPU rate soft caps

[Peter Williams <pwil3058@bigpond.net.au>]

Con Kolivas wrote:
> On Sunday 18 June 2006 18:26, Peter Williams wrote:
>> 3. Thanks to suggestions from Con Kolivas with respect to alternative
>> methods to reduce the possibility of a task being starved of CPU while
>> holding an important system resource, enforcement of caps is now
>> quite strict.  However, there will still be occasions where caps may be
>> exceeded due to this mechanism vetoing enforcement.
> 
> I hate to do this to you again but the mutexes held count advice I gave was 
> slightly off :|
>>  int fastcall __sched mutex_lock_interruptible(struct mutex *lock)
>>  {
>> +	int ret;
>> +
>>  	might_sleep();
>> -	return __mutex_fastpath_lock_retval
>> +	ret = __mutex_fastpath_lock_retval
>>  			(&lock->count, __mutex_lock_interruptible_slowpath);
>> +
>> +	if (!ret)
>> +		inc_mutex_count();
>> +
>> +	return ret;
>>  }
>>
>>  EXPORT_SYMBOL(mutex_lock_interruptible);
>> @@ -357,8 +381,13 @@ static inline int __mutex_trylock_slowpa
>>   */
>>  int fastcall __sched mutex_trylock(struct mutex *lock)
>>  {
>> -	return __mutex_fastpath_trylock(&lock->count,
>> +	int ret = __mutex_fastpath_trylock(&lock->count,
>>  					__mutex_trylock_slowpath);
>> +
>> +	if (!ret)
>> +		inc_mutex_count();
>> +
>> +	return ret;
> 
> See my track-mutexes-1.patch I recently posted.
> 
>  int fastcall __sched mutex_lock_interruptible(struct mutex *lock)
>  {
> +	int ret;
> +
>  	might_sleep();
> -	return __mutex_fastpath_lock_retval
> +	ret = __mutex_fastpath_lock_retval
>  			(&lock->count, __mutex_lock_interruptible_slowpath);
> +	if (likely(!ret))
> +		inc_mutex_count();
> +	return ret;
>  }
>  
>  EXPORT_SYMBOL(mutex_lock_interruptible);
> @@ -308,8 +325,12 @@ static inline int __mutex_trylock_slowpa
>   */
>  int fastcall mutex_trylock(struct mutex *lock)
>  {
> -	return __mutex_fastpath_trylock(&lock->count,
> +	int ret = __mutex_fastpath_trylock(&lock->count,
>  					__mutex_trylock_slowpath);
> +
> +	if (likely(ret))
> +		inc_mutex_count();
> +	return ret;
>  }
> 
> Note the if !ret in mutex_lock_interruptible vs the if ret in mutex_trylock(
> 
> I really should have given you the original debugging code that went with it, 
> sorry.
> 

That's OK.  I should have read the comments above mutex_trylock() more 
carefully myself.

Thanks
Peter
PS Have you thought about merging these caps into staircase in lieu of 
SCHED_IDLEPRIO?  Hard caps should be easy and soft caps not much harder.
If that was available I could merge the caps patch with plugsched.
-- 
Peter Williams                                   pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
  -- Ambrose Bierce