From 435bef7a2fac8b100cc5259b25165db1c08da49d Mon Sep 17 00:00:00 2001
From: Mateusz Guzik <mjg@FreeBSD.org>
Date: Tue, 20 Nov 2018 14:58:41 +0000
Subject: [PATCH] Implement unr64

Important users of unr like tmpfs or pipes can get away with just
ever-increasing counters, making the overhead of managing the state
for 32 bit counters a pessimization.

Change it to an atomic variable. This can be further sped up by making
the counts variable "allocate" ranges and store them per-cpu.

Reviewed by:	kib
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D18054
---
 sys/kern/subr_unit.c | 13 +++++++++++++
 sys/sys/systm.h      | 26 ++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/sys/kern/subr_unit.c b/sys/kern/subr_unit.c
index f2eafad41175..9855deeba1b4 100644
--- a/sys/kern/subr_unit.c
+++ b/sys/kern/subr_unit.c
@@ -98,6 +98,19 @@ static struct mtx unitmtx;
 
 MTX_SYSINIT(unit, &unitmtx, "unit# allocation", MTX_DEF);
 
+#ifdef UNR64_LOCKED
+uint64_t
+alloc_unr64(struct unrhdr64 *unr64)
+{
+	uint64_t item;
+
+	mtx_lock(&unitmtx);
+	item = unr64->counter++;
+	mtx_unlock(&unitmtx);
+	return (item);
+}
+#endif
+
 #else /* ...USERLAND */
 
 #include <bitstring.h>
diff --git a/sys/sys/systm.h b/sys/sys/systm.h
index e02a4e3a34c5..a1b98c5660c2 100644
--- a/sys/sys/systm.h
+++ b/sys/sys/systm.h
@@ -523,6 +523,32 @@ int alloc_unr_specific(struct unrhdr *uh, u_int item);
 int alloc_unrl(struct unrhdr *uh);
 void free_unr(struct unrhdr *uh, u_int item);
 
+#if defined(__mips__) || defined(__powerpc__)
+#define UNR64_LOCKED
+#endif
+
+struct unrhdr64 {
+        uint64_t	counter;
+};
+
+static __inline void
+new_unrhdr64(struct unrhdr64 *unr64, uint64_t low)
+{
+
+	unr64->counter = low;
+}
+
+#ifdef UNR64_LOCKED
+uint64_t alloc_unr64(struct unrhdr64 *);
+#else
+static __inline uint64_t
+alloc_unr64(struct unrhdr64 *unr64)
+{
+
+	return (atomic_fetchadd_64(&unr64->counter, 1));
+}
+#endif
+
 void	intr_prof_stack_use(struct thread *td, struct trapframe *frame);
 
 void counted_warning(unsigned *counter, const char *msg);