xen: add debugfs support

Add support for exporting statistics on mmu updates, multicall
batching and pv spinlocks into debugfs. The base path is xen/ and
each subsystem adds its own directory: mmu, multicalls, spinlocks.

In each directory, writing 1 to "zero_stats" will cause the
corresponding stats to be zeroed the next time they're updated.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Acked-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 162 insertions, 3 deletions

diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 4884bc603aa..0d8f3b2d9be 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -4,6 +4,8 @@
  */
 #include <linux/kernel_stat.h>
 #include <linux/spinlock.h>
+#include <linux/debugfs.h>
+#include <linux/log2.h>
 
 #include <asm/paravirt.h>
 
@@ -11,6 +13,93 @@
 #include <xen/events.h>
 
 #include "xen-ops.h"
+#include "debugfs.h"
+
+#ifdef CONFIG_XEN_DEBUG_FS
+static struct xen_spinlock_stats
+{
+	u64 taken;
+	u32 taken_slow;
+	u32 taken_slow_nested;
+	u32 taken_slow_pickup;
+	u32 taken_slow_spurious;
+
+	u64 released;
+	u32 released_slow;
+	u32 released_slow_kicked;
+
+#define HISTO_BUCKETS	20
+	u32 histo_spin_fast[HISTO_BUCKETS+1];
+	u32 histo_spin[HISTO_BUCKETS+1];
+
+	u64 spinning_time;
+	u64 total_time;
+} spinlock_stats;
+
+static u8 zero_stats;
+
+static unsigned lock_timeout = 1 << 10;
+#define TIMEOUT lock_timeout
+
+static inline void check_zero(void)
+{
+	if (unlikely(zero_stats)) {
+		memset(&spinlock_stats, 0, sizeof(spinlock_stats));
+		zero_stats = 0;
+	}
+}
+
+#define ADD_STATS(elem, val)			\
+	do { check_zero(); spinlock_stats.elem += (val); } while(0)
+
+static inline u64 spin_time_start(void)
+{
+	return xen_clocksource_read();
+}
+
+static void __spin_time_accum(u64 delta, u32 *array)
+{
+	unsigned index = ilog2(delta);
+
+	check_zero();
+
+	if (index < HISTO_BUCKETS)
+		array[index]++;
+	else
+		array[HISTO_BUCKETS]++;
+}
+
+static inline void spin_time_accum_fast(u64 start)
+{
+	u32 delta = xen_clocksource_read() - start;
+
+	__spin_time_accum(delta, spinlock_stats.histo_spin_fast);
+	spinlock_stats.spinning_time += delta;
+}
+
+static inline void spin_time_accum(u64 start)
+{
+	u32 delta = xen_clocksource_read() - start;
+
+	__spin_time_accum(delta, spinlock_stats.histo_spin);
+	spinlock_stats.total_time += delta;
+}
+#else  /* !CONFIG_XEN_DEBUG_FS */
+#define TIMEOUT			(1 << 10)
+#define ADD_STATS(elem, val)	do { (void)(val); } while(0)
+
+static inline u64 spin_time_start(void)
+{
+	return 0;
+}
+
+static inline void spin_time_accum_fast(u64 start)
+{
+}
+static inline void spin_time_accum(u64 start)
+{
+}
+#endif  /* CONFIG_XEN_DEBUG_FS */
 
 struct xen_spinlock {
 	unsigned char lock;		/* 0 -> free; 1 -> locked */
@@ -92,6 +181,9 @@ static noinline int xen_spin_lock_slow(struct raw_spinlock *lock)
 	/* announce we're spinning */
 	prev = spinning_lock(xl);
 
+	ADD_STATS(taken_slow, 1);
+	ADD_STATS(taken_slow_nested, prev != NULL);
+
 	do {
 		/* clear pending */
 		xen_clear_irq_pending(irq);
@@ -100,6 +192,8 @@ static noinline int xen_spin_lock_slow(struct raw_spinlock *lock)
 		   we weren't looking  */
 		ret = xen_spin_trylock(lock);
 		if (ret) {
+			ADD_STATS(taken_slow_pickup, 1);
+
 			/*
 			 * If we interrupted another spinlock while it
 			 * was blocking, make sure it doesn't block
@@ -120,6 +214,7 @@ static noinline int xen_spin_lock_slow(struct raw_spinlock *lock)
 		 * pending.
 		 */
 		xen_poll_irq(irq);
+		ADD_STATS(taken_slow_spurious, !xen_test_irq_pending(irq));
 	} while (!xen_test_irq_pending(irq)); /* check for spurious wakeups */
 
 	kstat_this_cpu.irqs[irq]++;
@@ -132,11 +227,18 @@ out:
 static void xen_spin_lock(struct raw_spinlock *lock)
 {
 	struct xen_spinlock *xl = (struct xen_spinlock *)lock;
-	int timeout;
+	unsigned timeout;
 	u8 oldval;
+	u64 start_spin;
+
+	ADD_STATS(taken, 1);
+
+	start_spin = spin_time_start();
 
 	do {
-		timeout = 1 << 10;
+		u64 start_spin_fast = spin_time_start();
+
+		timeout = TIMEOUT;
 
 		asm("1: xchgb %1,%0\n"
 		    "   testb %1,%1\n"
@@ -151,16 +253,22 @@ static void xen_spin_lock(struct raw_spinlock *lock)
 		    : "1" (1)
 		    : "memory");
 
-	} while (unlikely(oldval != 0 && !xen_spin_lock_slow(lock)));
+		spin_time_accum_fast(start_spin_fast);
+	} while (unlikely(oldval != 0 && (TIMEOUT == ~0 || !xen_spin_lock_slow(lock))));
+
+	spin_time_accum(start_spin);
 }
 
 static noinline void xen_spin_unlock_slow(struct xen_spinlock *xl)
 {
 	int cpu;
 
+	ADD_STATS(released_slow, 1);
+
 	for_each_online_cpu(cpu) {
 		/* XXX should mix up next cpu selection */
 		if (per_cpu(lock_spinners, cpu) == xl) {
+			ADD_STATS(released_slow_kicked, 1);
 			xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
 			break;
 		}
@@ -171,6 +279,8 @@ static void xen_spin_unlock(struct raw_spinlock *lock)
 {
 	struct xen_spinlock *xl = (struct xen_spinlock *)lock;
 
+	ADD_STATS(released, 1);
+
 	smp_wmb();		/* make sure no writes get moved after unlock */
 	xl->lock = 0;		/* release lock */
 
@@ -216,3 +326,52 @@ void __init xen_init_spinlocks(void)
 	pv_lock_ops.spin_trylock = xen_spin_trylock;
 	pv_lock_ops.spin_unlock = xen_spin_unlock;
 }
+
+#ifdef CONFIG_XEN_DEBUG_FS
+
+static struct dentry *d_spin_debug;
+
+static int __init xen_spinlock_debugfs(void)
+{
+	struct dentry *d_xen = xen_init_debugfs();
+
+	if (d_xen == NULL)
+		return -ENOMEM;
+
+	d_spin_debug = debugfs_create_dir("spinlocks", d_xen);
+
+	debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
+
+	debugfs_create_u32("timeout", 0644, d_spin_debug, &lock_timeout);
+
+	debugfs_create_u64("taken", 0444, d_spin_debug, &spinlock_stats.taken);
+	debugfs_create_u32("taken_slow", 0444, d_spin_debug,
+			   &spinlock_stats.taken_slow);
+	debugfs_create_u32("taken_slow_nested", 0444, d_spin_debug,
+			   &spinlock_stats.taken_slow_nested);
+	debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
+			   &spinlock_stats.taken_slow_pickup);
+	debugfs_create_u32("taken_slow_spurious", 0444, d_spin_debug,
+			   &spinlock_stats.taken_slow_spurious);
+
+	debugfs_create_u64("released", 0444, d_spin_debug, &spinlock_stats.released);
+	debugfs_create_u32("released_slow", 0444, d_spin_debug,
+			   &spinlock_stats.released_slow);
+	debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
+			   &spinlock_stats.released_slow_kicked);
+
+	debugfs_create_u64("time_spinning", 0444, d_spin_debug,
+			   &spinlock_stats.spinning_time);
+	debugfs_create_u64("time_total", 0444, d_spin_debug,
+			   &spinlock_stats.total_time);
+
+	xen_debugfs_create_u32_array("histo_total", 0444, d_spin_debug,
+				     spinlock_stats.histo_spin, HISTO_BUCKETS + 1);
+	xen_debugfs_create_u32_array("histo_spinning", 0444, d_spin_debug,
+				     spinlock_stats.histo_spin_fast, HISTO_BUCKETS + 1);
+
+	return 0;
+}
+fs_initcall(xen_spinlock_debugfs);
+
+#endif	/* CONFIG_XEN_DEBUG_FS */