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Commit 7ba5c840 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Ingo Molnar
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rcu: Add __rcu_pending tracing to hierarchical RCU 



Add tracing to __rcu_pending() to provide information on why RCU
processing was kicked off.  This is helpful for debugging hierarchical
RCU, and might also be helpful in learning how hierarchical RCU operates.

Located-by: default avatarAnton Blanchard <anton@au1.ibm.com>
Tested-by: default avatarAnton Blanchard <anton@au1.ibm.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: anton@samba.org
Cc: akpm@linux-foundation.org
Cc: dipankar@in.ibm.com
Cc: manfred@colorfullife.com
Cc: cl@linux-foundation.org
Cc: josht@linux.vnet.ibm.com
Cc: schamp@sgi.com
Cc: niv@us.ibm.com
Cc: dvhltc@us.ibm.com
Cc: ego@in.ibm.com
Cc: laijs@cn.fujitsu.com
Cc: rostedt@goodmis.org
Cc: peterz@infradead.org
Cc: penberg@cs.helsinki.fi
Cc: andi@firstfloor.org
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
LKML-Reference: <1239683479943-git-send-email->
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 05cfbd66

include/linux/rcutree.h

+8 −1
Original line number Diff line number Diff line
@@ -161,8 +161,15 @@ struct rcu_data { 
	unsigned long offline_fqs;	/* Kicked due to being offline. */

	unsigned long resched_ipi;	/* Sent a resched IPI. */



	/* 5) For future __rcu_pending statistics. */

	/* 5) __rcu_pending() statistics. */

	long n_rcu_pending;		/* rcu_pending() calls since boot. */

	long n_rp_qs_pending;

	long n_rp_cb_ready;

	long n_rp_cpu_needs_gp;

	long n_rp_gp_completed;

	long n_rp_gp_started;

	long n_rp_need_fqs;

	long n_rp_need_nothing;



	int cpu;

};

kernel/rcutree.c

+19 −6
Original line number Diff line number Diff line
@@ -1259,31 +1259,44 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) 
	check_cpu_stall(rsp, rdp);



	/* Is the RCU core waiting for a quiescent state from this CPU? */

	if (rdp->qs_pending)

	if (rdp->qs_pending) {

		rdp->n_rp_qs_pending++;

		return 1;

	}



	/* Does this CPU have callbacks ready to invoke? */

	if (cpu_has_callbacks_ready_to_invoke(rdp))

	if (cpu_has_callbacks_ready_to_invoke(rdp)) {

		rdp->n_rp_cb_ready++;

		return 1;

	}



	/* Has RCU gone idle with this CPU needing another grace period? */

	if (cpu_needs_another_gp(rsp, rdp))

	if (cpu_needs_another_gp(rsp, rdp)) {

		rdp->n_rp_cpu_needs_gp++;

		return 1;

	}



	/* Has another RCU grace period completed?  */

	if (ACCESS_ONCE(rsp->completed) != rdp->completed) /* outside of lock */

	if (ACCESS_ONCE(rsp->completed) != rdp->completed) { /* outside lock */

		rdp->n_rp_gp_completed++;

		return 1;

	}



	/* Has a new RCU grace period started? */

	if (ACCESS_ONCE(rsp->gpnum) != rdp->gpnum) /* outside of lock */

	if (ACCESS_ONCE(rsp->gpnum) != rdp->gpnum) { /* outside lock */

		rdp->n_rp_gp_started++;

		return 1;

	}



	/* Has an RCU GP gone long enough to send resched IPIs &c? */

	if (ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum) &&

	    ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0))

	    ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)) {

		rdp->n_rp_need_fqs++;

		return 1;

	}



	/* nothing to do */

	rdp->n_rp_need_nothing++;

	return 0;

}

kernel/rcutree_trace.c

+63 −1
Original line number Diff line number Diff line
@@ -213,7 +213,63 @@ static struct file_operations rcugp_fops = { 
	.release = single_release,

};



static struct dentry *rcudir, *datadir, *datadir_csv, *hierdir, *gpdir;

static void print_one_rcu_pending(struct seq_file *m, struct rcu_data *rdp)

{

	seq_printf(m, "%3d%cnp=%ld "

		   "qsp=%ld cbr=%ld cng=%ld gpc=%ld gps=%ld nf=%ld nn=%ld\n",

		   rdp->cpu,

		   cpu_is_offline(rdp->cpu) ? '!' : ' ',

		   rdp->n_rcu_pending,

		   rdp->n_rp_qs_pending,

		   rdp->n_rp_cb_ready,

		   rdp->n_rp_cpu_needs_gp,

		   rdp->n_rp_gp_completed,

		   rdp->n_rp_gp_started,

		   rdp->n_rp_need_fqs,

		   rdp->n_rp_need_nothing);

}



static void print_rcu_pendings(struct seq_file *m, struct rcu_state *rsp)

{

	int cpu;

	struct rcu_data *rdp;



	for_each_possible_cpu(cpu) {

		rdp = rsp->rda[cpu];

		if (rdp->beenonline)

			print_one_rcu_pending(m, rdp);

	}

}



static int show_rcu_pending(struct seq_file *m, void *unused)

{

	seq_puts(m, "rcu:\n");

	print_rcu_pendings(m, &rcu_state);

	seq_puts(m, "rcu_bh:\n");

	print_rcu_pendings(m, &rcu_bh_state);

	return 0;

}



static int rcu_pending_open(struct inode *inode, struct file *file)

{

	return single_open(file, show_rcu_pending, NULL);

}



static struct file_operations rcu_pending_fops = {

	.owner = THIS_MODULE,

	.open = rcu_pending_open,

	.read = seq_read,

	.llseek = seq_lseek,

	.release = single_release,

};



static struct dentry *rcudir;

static struct dentry *datadir;

static struct dentry *datadir_csv;

static struct dentry *gpdir;

static struct dentry *hierdir;

static struct dentry *rcu_pendingdir;



static int __init rcuclassic_trace_init(void)

{

	rcudir = debugfs_create_dir("rcu", NULL);
@@ -238,6 +294,11 @@ static int __init rcuclassic_trace_init(void) 
						NULL, &rcuhier_fops);

	if (!hierdir)

		goto free_out;



	rcu_pendingdir = debugfs_create_file("rcu_pending", 0444, rcudir,

						NULL, &rcu_pending_fops);

	if (!rcu_pendingdir)

		goto free_out;

	return 0;

free_out:

	if (datadir)
@@ -257,6 +318,7 @@ static void __exit rcuclassic_trace_cleanup(void) 
	debugfs_remove(datadir_csv);

	debugfs_remove(gpdir);

	debugfs_remove(hierdir);

	debugfs_remove(rcu_pendingdir);

	debugfs_remove(rcudir);

}