Convert locking used within taskstats interface and delay accounting
code to be more fine-grained.
Dynamic allocation of the delays data structure led to exit race
conditions that were being fixed through use of a global mutex at the
taskstats interface level. The same mutex was also being used for
protecting per-task delay structure allocation. Together, these were
causing higher contention and unnecessary serialization.
This patch switches to a per-task locking for protecting tsk->delays
and eliminates global locking within the taskstats interface.
Results collected by Jay Lan ([email protected]) from running a test
with rapid forks/exits shows substantial improvement in system time.
For a benchmark that only forks+exits 1000 threads and runs for
5000 iterations, the reduction seen are as follows:
base +patch %improvement
user 0.06 0.07 -16%
system 1.34 0.86 35%
elapsed 622 470 24%
Signed-off-by: Shailabh Nagar <[email protected]>
---
include/linux/sched.h | 1 +
kernel/delayacct.c | 18 ++++++++++++++++--
kernel/taskstats.c | 7 -------
3 files changed, 17 insertions(+), 9 deletions(-)
Index: linux-2.6.17/include/linux/sched.h
===================================================================
--- linux-2.6.17.orig/include/linux/sched.h 2006-06-22 02:56:44.000000000 -0400
+++ linux-2.6.17/include/linux/sched.h 2006-06-22 15:18:09.000000000 -0400
@@ -933,6 +933,7 @@ struct task_struct {
*/
struct pipe_inode_info *splice_pipe;
#ifdef CONFIG_TASK_DELAY_ACCT
+ spinlock_t delays_lock;
struct task_delay_info *delays;
#endif
};
Index: linux-2.6.17/kernel/delayacct.c
===================================================================
--- linux-2.6.17.orig/kernel/delayacct.c 2006-06-22 02:56:44.000000000 -0400
+++ linux-2.6.17/kernel/delayacct.c 2006-06-22 15:18:09.000000000 -0400
@@ -41,6 +41,10 @@ void delayacct_init(void)
void __delayacct_tsk_init(struct task_struct *tsk)
{
+ spin_lock_init(&tsk->delays_lock);
+ /* No need to acquire tsk->delays_lock for allocation here unless
+ __delayacct_tsk_init called after tsk is attached to tasklist
+ */
tsk->delays = kmem_cache_zalloc(delayacct_cache, SLAB_KERNEL);
if (tsk->delays)
spin_lock_init(&tsk->delays->lock);
@@ -49,9 +53,9 @@ void __delayacct_tsk_init(struct task_st
void __delayacct_tsk_exit(struct task_struct *tsk)
{
struct task_delay_info *delays = tsk->delays;
- mutex_lock(&taskstats_exit_mutex);
+ spin_lock(&tsk->delays_lock);
tsk->delays = NULL;
- mutex_unlock(&taskstats_exit_mutex);
+ spin_unlock(&tsk->delays_lock);
kmem_cache_free(delayacct_cache, delays);
}
@@ -114,6 +118,14 @@ int __delayacct_add_tsk(struct taskstats
struct timespec ts;
unsigned long t1,t2,t3;
+ spin_lock(&tsk->delays_lock);
+
+ /* Though tsk->delays accessed later, early exit avoids
+ * unnecessary returning of other data
+ */
+ if (!tsk->delays)
+ goto done;
+
tmp = (s64)d->cpu_run_real_total;
cputime_to_timespec(tsk->utime + tsk->stime, &ts);
tmp += timespec_to_ns(&ts);
@@ -148,6 +160,8 @@ int __delayacct_add_tsk(struct taskstats
d->swapin_count += tsk->delays->swapin_count;
spin_unlock(&tsk->delays->lock);
+done:
+ spin_unlock(&tsk->delays_lock);
return 0;
}
Index: linux-2.6.17/kernel/taskstats.c
===================================================================
--- linux-2.6.17.orig/kernel/taskstats.c 2006-06-22 02:56:44.000000000 -0400
+++ linux-2.6.17/kernel/taskstats.c 2006-06-22 15:27:09.000000000 -0400
@@ -25,7 +25,6 @@
static DEFINE_PER_CPU(__u32, taskstats_seqnum) = { 0 };
static int family_registered = 0;
kmem_cache_t *taskstats_cache;
-DEFINE_MUTEX(taskstats_exit_mutex);
static struct genl_family family = {
.id = GENL_ID_GENERATE,
@@ -193,7 +192,6 @@ static int taskstats_send_stats(struct s
if (rc < 0)
return rc;
- mutex_lock(&taskstats_exit_mutex);
if (info->attrs[TASKSTATS_CMD_ATTR_PID]) {
u32 pid = nla_get_u32(info->attrs[TASKSTATS_CMD_ATTR_PID]);
rc = fill_pid(pid, NULL, &stats);
@@ -219,7 +217,6 @@ static int taskstats_send_stats(struct s
goto err;
}
- mutex_unlock(&taskstats_exit_mutex);
nla_nest_end(rep_skb, na);
return send_reply(rep_skb, info->snd_pid, TASKSTATS_MSG_UNICAST);
@@ -228,7 +225,6 @@ nla_put_failure:
return genlmsg_cancel(rep_skb, reply);
err:
nlmsg_free(rep_skb);
- mutex_unlock(&taskstats_exit_mutex);
return rc;
}
@@ -246,8 +242,6 @@ void taskstats_exit_send(struct task_str
if (!family_registered || !tidstats)
return;
- mutex_lock(&taskstats_exit_mutex);
-
is_thread_group = !thread_group_empty(tsk);
rc = 0;
@@ -305,7 +299,6 @@ nla_put_failure:
err_skb:
nlmsg_free(rep_skb);
ret:
- mutex_unlock(&taskstats_exit_mutex);
return;
}
-
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