[Xenomai-core] [PATCH 1/2] /proc output - improve scalability

[Jan Kiszka <jan.kiszka@domain.hid>]

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This is an unmodified resent of my previously posted patch to make
/proc/xenomai/{sched,stat} O(1) wrt nklock. It also solve a potential race during
thread cleanup when accessing the dying thread's name.

Jan


---
 include/nucleus/pod.h |    1 
 ksrc/nucleus/module.c |   94 +++++++++++++++++++++++++++++++++-----------------
 ksrc/nucleus/pod.c    |    2 +
 3 files changed, 66 insertions(+), 31 deletions(-)

Index: xenomai/include/nucleus/pod.h
===================================================================
--- xenomai.orig/include/nucleus/pod.h
+++ xenomai/include/nucleus/pod.h
@@ -195,6 +195,7 @@ struct xnpod {
     xnsched_t sched[XNARCH_NR_CPUS]; /*!< Per-cpu scheduler slots. */
 
     xnqueue_t threadq;          /*!< All existing threads. */
+    int threadq_rev;            /*!< Modification counter of threadq. */
 
     volatile u_long schedlck;	/*!< Scheduler lock count. */
 
Index: xenomai/ksrc/nucleus/module.c
===================================================================
--- xenomai.orig/ksrc/nucleus/module.c
+++ xenomai/ksrc/nucleus/module.c
@@ -99,7 +99,7 @@ struct sched_seq_iterator {
 	struct sched_seq_info {
 		int cpu;
 		pid_t pid;
-		const char *name;
+		char name[XNOBJECT_NAME_LEN];
 		int cprio;
 		xnticks_t timeout;
 		xnflags_t status;
@@ -177,17 +177,26 @@ static struct seq_operations sched_op = 
 
 static int sched_seq_open(struct inode *inode, struct file *file)
 {
-	struct sched_seq_iterator *iter;
+	struct sched_seq_iterator *iter = NULL;
 	struct seq_file *seq;
 	xnholder_t *holder;
-	int err, count;
+	int err, count, rev;
 	spl_t s;
 
 	if (!nkpod)
 		return -ESRCH;
 
+      restart:
+	xnlock_get_irqsave(&nklock, s);
+
+	rev = nkpod->threadq_rev;
 	count = countq(&nkpod->threadq);	/* Cannot be empty (ROOT) */
+	holder = getheadq(&nkpod->threadq);
+
+	xnlock_put_irqrestore(&nklock, s);
 
+	if (iter)
+		kfree(iter);
 	iter = kmalloc(sizeof(*iter)
 		       + (count - 1) * sizeof(struct sched_seq_info),
 		       GFP_KERNEL);
@@ -202,31 +211,37 @@ static int sched_seq_open(struct inode *
 	}
 
 	iter->nentries = 0;
+	iter->start_time = xntimer_get_jiffies();
 
-	/* Take a snapshot and release the nucleus lock immediately after,
-	   so that dumping /proc/xenomai/sched with lots of entries won't
-	   cause massive jittery. */
+	/* Take a snapshot element-wise, restart if something changes
+	   underneath us. */
 
-	xnlock_get_irqsave(&nklock, s);
+	while (holder) {
+		xnthread_t *thread;
+		int n;
 
-	iter->start_time = xntimer_get_jiffies();
+		xnlock_get_irqsave(&nklock, s);
+
+		if (nkpod->threadq_rev != rev)
+			goto restart;
+		rev = nkpod->threadq_rev;
 
-	for (holder = getheadq(&nkpod->threadq);
-	     holder && count > 0;
-	     holder = nextq(&nkpod->threadq, holder), count--) {
-		xnthread_t *thread = link2thread(holder, glink);
-		int n = iter->nentries++;
+		thread = link2thread(holder, glink);
+		n = iter->nentries++;
 
 		iter->sched_info[n].cpu = xnsched_cpu(thread->sched);
 		iter->sched_info[n].pid = xnthread_user_pid(thread);
-		iter->sched_info[n].name = thread->name;
+		memcpy(iter->sched_info[n].name, thread->name,
+		       sizeof(iter->sched_info[n].name));
 		iter->sched_info[n].cprio = thread->cprio;
 		iter->sched_info[n].timeout =
 		    xnthread_get_timeout(thread, iter->start_time);
 		iter->sched_info[n].status = thread->status;
-	}
 
-	xnlock_put_irqrestore(&nklock, s);
+		holder = nextq(&nkpod->threadq, holder);
+
+		xnlock_put_irqrestore(&nklock, s);
+	}
 
 	seq = (struct seq_file *)file->private_data;
 	seq->private = iter;
@@ -250,7 +265,7 @@ struct stat_seq_iterator {
 		int cpu;
 		pid_t pid;
 		xnflags_t status;
-		const char *name;
+		char name[XNOBJECT_NAME_LEN];
 		unsigned long ssw;
 		unsigned long csw;
 		unsigned long pf;
@@ -315,17 +330,26 @@ static struct seq_operations stat_op = {
 
 static int stat_seq_open(struct inode *inode, struct file *file)
 {
-	struct stat_seq_iterator *iter;
+	struct stat_seq_iterator *iter = NULL;
 	struct seq_file *seq;
 	xnholder_t *holder;
-	int err, count;
+	int err, count, rev;
 	spl_t s;
 
 	if (!nkpod)
 		return -ESRCH;
 
+      restart:
+	xnlock_get_irqsave(&nklock, s);
+
+	rev = nkpod->threadq_rev;
 	count = countq(&nkpod->threadq);	/* Cannot be empty (ROOT) */
+	holder = getheadq(&nkpod->threadq);
+
+	xnlock_put_irqrestore(&nklock, s);
 
+	if (iter)
+		kfree(iter);
 	iter = kmalloc(sizeof(*iter)
 		       + (count - 1) * sizeof(struct stat_seq_info),
 		       GFP_KERNEL);
@@ -341,27 +365,35 @@ static int stat_seq_open(struct inode *i
 
 	iter->nentries = 0;
 
-	/* Take a snapshot and release the nucleus lock immediately after,
-	   so that dumping /proc/xenomai/stat with lots of entries won't
-	   cause massive jittery. */
+	/* Take a snapshot element-wise, restart if something changes
+	   underneath us. */
 
-	xnlock_get_irqsave(&nklock, s);
+	while (holder) {
+		xnthread_t *thread;
+		int n;
+
+		xnlock_get_irqsave(&nklock, s);
+
+		if (nkpod->threadq_rev != rev)
+			goto restart;
+		rev = nkpod->threadq_rev;
+
+		thread = link2thread(holder, glink);
+		n = iter->nentries++;
 
-	for (holder = getheadq(&nkpod->threadq);
-	     holder && count > 0;
-	     holder = nextq(&nkpod->threadq, holder), count--) {
-		xnthread_t *thread = link2thread(holder, glink);
-		int n = iter->nentries++;
 		iter->stat_info[n].cpu = xnsched_cpu(thread->sched);
 		iter->stat_info[n].pid = xnthread_user_pid(thread);
-		iter->stat_info[n].name = thread->name;
+		memcpy(iter->stat_info[n].name, thread->name,
+		       sizeof(iter->stat_info[n].name));
 		iter->stat_info[n].status = thread->status;
 		iter->stat_info[n].ssw = thread->stat.ssw;
 		iter->stat_info[n].csw = thread->stat.csw;
 		iter->stat_info[n].pf = thread->stat.pf;
-	}
 
-	xnlock_put_irqrestore(&nklock, s);
+		holder = nextq(&nkpod->threadq, holder);
+
+		xnlock_put_irqrestore(&nklock, s);
+	}
 
 	seq = (struct seq_file *)file->private_data;
 	seq->private = iter;
Index: xenomai/ksrc/nucleus/pod.c
===================================================================
--- xenomai.orig/ksrc/nucleus/pod.c
+++ xenomai/ksrc/nucleus/pod.c
@@ -815,6 +815,7 @@ int xnpod_init_thread(xnthread_t *thread
 	xnlock_get_irqsave(&nklock, s);
 	thread->sched = xnpod_current_sched();
 	appendq(&nkpod->threadq, &thread->glink);
+	nkpod->threadq_rev++;
 	xnpod_suspend_thread(thread, XNDORMANT | (flags & XNSUSP), XN_INFINITE,
 			     NULL);
 	xnlock_put_irqrestore(&nklock, s);
@@ -1225,6 +1226,7 @@ void xnpod_delete_thread(xnthread_t *thr
 	sched = thread->sched;
 
 	removeq(&nkpod->threadq, &thread->glink);
+	nkpod->threadq_rev++;
 
 	if (!testbits(thread->status, XNTHREAD_BLOCK_BITS)) {
 		if (testbits(thread->status, XNREADY)) {






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