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Commit b3426599 authored by Paul Jackson's avatar Paul Jackson Committed by Linus Torvalds
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[PATCH] cpuset semaphore depth check optimize 



Optimize the deadlock avoidance check on the global cpuset
semaphore cpuset_sem.  Instead of adding a depth counter to the
task struct of each task, rather just two words are enough, one
to store the depth and the other the current cpuset_sem holder.

Thanks to Nikita Danilov for the idea.

Signed-off-by: default avatarPaul Jackson <pj@sgi.com>

[ We may want to change this further, but at least it's now
  a totally internal decision to the cpusets code ]

Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent f24ec7f6

include/linux/sched.h

+0 −1
Original line number Diff line number Diff line
@@ -785,7 +785,6 @@ struct task_struct { 
	short il_next;

#endif

#ifdef CONFIG_CPUSETS

	short cpuset_sem_nest_depth;

	struct cpuset *cpuset;

	nodemask_t mems_allowed;

	int cpuset_mems_generation;

kernel/cpuset.c

+9 −4
Original line number Diff line number Diff line
@@ -180,6 +180,8 @@ static struct super_block *cpuset_sb = NULL; 
 */



static DECLARE_MUTEX(cpuset_sem);

static struct task_struct *cpuset_sem_owner;

static int cpuset_sem_depth;



/*

 * The global cpuset semaphore cpuset_sem can be needed by the
@@ -200,17 +202,20 @@ static DECLARE_MUTEX(cpuset_sem); 


static inline void cpuset_down(struct semaphore *psem)

{

	if (current->cpuset_sem_nest_depth == 0)

	if (cpuset_sem_owner != current) {

		down(psem);

	current->cpuset_sem_nest_depth++;

		cpuset_sem_owner = current;

	}

	cpuset_sem_depth++;

}



static inline void cpuset_up(struct semaphore *psem)

{

	current->cpuset_sem_nest_depth--;

	if (current->cpuset_sem_nest_depth == 0)

	if (--cpuset_sem_depth == 0) {

		cpuset_sem_owner = NULL;

		up(psem);

	}

}



/*

 * A couple of forward declarations required, due to cyclic reference loop: