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Subject[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: Paul Jackson <pj@sgi.com>

Index: linux-2.6.13-mem_exclusive_oom/include/linux/sched.h
===================================================================
--- linux-2.6.13-mem_exclusive_oom.orig/include/linux/sched.h
+++ linux-2.6.13-mem_exclusive_oom/include/linux/sched.h
@@ -765,7 +765,6 @@ 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;
Index: linux-2.6.13-mem_exclusive_oom/kernel/cpuset.c
===================================================================
--- linux-2.6.13-mem_exclusive_oom.orig/kernel/cpuset.c
+++ linux-2.6.13-mem_exclusive_oom/kernel/cpuset.c
@@ -180,6 +180,8 @@ static struct super_block *cpuset_sb = N
*/

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
@@ -200,16 +202,19 @@ 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);
+ }
}

/*
--
I won't rest till it's the best ...
Programmer, Linux Scalability
Paul Jackson <pj@sgi.com> 1.650.933.1373
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