From 0d2224733e970aaa67a4e1af7b340044adda92f6 Mon Sep 17 00:00:00 2001
From: Mitchell Horne <mhorne@FreeBSD.org>
Date: Thu, 25 Nov 2021 12:01:11 -0400
Subject: [PATCH] Implement GET_STACK_USAGE on remaining archs

This definition enables callers to estimate remaining space on the
kstack, and take action on it. Notably, it enables optimizations in the
GEOM and netgraph subsystems to directly dispatch work items when there
is sufficient stack space, rather than queuing them for a worker thread.

Implement it for riscv, arm, and mips. Remove the #ifdefs, so it will
not go unimplemented elsewhere.

PR:		259157
Reviewed by:	mav, kib, markj (previous version)
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D32580
---
 sys/arm/include/proc.h   | 11 +++++++++++
 sys/geom/geom_io.c       |  8 --------
 sys/mips/include/proc.h  | 11 +++++++++++
 sys/netgraph/ng_base.c   |  3 +--
 sys/riscv/include/proc.h | 11 +++++++++++
 5 files changed, 34 insertions(+), 10 deletions(-)

diff --git a/sys/arm/include/proc.h b/sys/arm/include/proc.h
index 641b4228004..5b3b9286363 100644
--- a/sys/arm/include/proc.h
+++ b/sys/arm/include/proc.h
@@ -72,4 +72,15 @@ struct syscall_args {
 	register_t args[MAXARGS];
 } __aligned(8);
 
+#ifdef _KERNEL
+#include <machine/pcb.h>
+
+/* Get the current kernel thread stack usage. */
+#define	GET_STACK_USAGE(total, used) do {				\
+	struct thread *td = curthread;					\
+	(total) = td->td_kstack_pages * PAGE_SIZE - sizeof(struct pcb);	\
+	(used) = td->td_kstack + (total) - (vm_offset_t)&td;		\
+} while (0)
+
+#endif  /* _KERNEL */
 #endif /* !_MACHINE_PROC_H_ */
diff --git a/sys/geom/geom_io.c b/sys/geom/geom_io.c
index f32a3dc52f9..ce7f6c86738 100644
--- a/sys/geom/geom_io.c
+++ b/sys/geom/geom_io.c
@@ -559,7 +559,6 @@ g_io_request(struct bio *bp, struct g_consumer *cp)
 	atomic_add_int(&cp->nstart, 1);
 #endif
 
-#ifdef GET_STACK_USAGE
 	direct = (cp->flags & G_CF_DIRECT_SEND) != 0 &&
 	    (pp->flags & G_PF_DIRECT_RECEIVE) != 0 &&
 	    !g_is_geom_thread(curthread) &&
@@ -573,9 +572,6 @@ g_io_request(struct bio *bp, struct g_consumer *cp)
 		if (su * 2 > st)
 			direct = 0;
 	}
-#else
-	direct = 0;
-#endif
 
 	if (direct) {
 		error = g_io_check(bp);
@@ -655,7 +651,6 @@ g_io_deliver(struct bio *bp, int error)
 	bp->bio_bcount = bp->bio_length;
 	bp->bio_resid = bp->bio_bcount - bp->bio_completed;
 
-#ifdef GET_STACK_USAGE
 	direct = (pp->flags & G_PF_DIRECT_SEND) &&
 		 (cp->flags & G_CF_DIRECT_RECEIVE) &&
 		 !g_is_geom_thread(curthread);
@@ -666,9 +661,6 @@ g_io_deliver(struct bio *bp, int error)
 		if (su * 2 > st)
 			direct = 0;
 	}
-#else
-	direct = 0;
-#endif
 
 	/*
 	 * The statistics collection is lockless, as such, but we
diff --git a/sys/mips/include/proc.h b/sys/mips/include/proc.h
index 29d832a162e..5c8bc9d934e 100644
--- a/sys/mips/include/proc.h
+++ b/sys/mips/include/proc.h
@@ -96,4 +96,15 @@ struct syscall_args {
 #define	KINFO_PROC_SIZE 816
 #endif
 
+#ifdef _KERNEL
+#include <machine/pcb.h>
+
+/* Get the current kernel thread stack usage. */
+#define	GET_STACK_USAGE(total, used) do {				\
+	struct thread *td = curthread;					\
+	(total) = td->td_kstack_pages * PAGE_SIZE - sizeof(struct pcb);	\
+	(used) = td->td_kstack + (total) - (vm_offset_t)&td;		\
+} while (0)
+
+#endif  /* _KERNEL */
 #endif	/* !_MACHINE_PROC_H_ */
diff --git a/sys/netgraph/ng_base.c b/sys/netgraph/ng_base.c
index 655761c2f89..0d64000ee1f 100644
--- a/sys/netgraph/ng_base.c
+++ b/sys/netgraph/ng_base.c
@@ -2281,7 +2281,7 @@ ng_snd_item(item_p item, int flags)
 		queue = 1;
 	} else {
 		queue = 0;
-#ifdef GET_STACK_USAGE
+
 		/*
 		 * Most of netgraph nodes have small stack consumption and
 		 * for them 25% of free stack space is more than enough.
@@ -2296,7 +2296,6 @@ ng_snd_item(item_p item, int flags)
 		    ((node->nd_flags & NGF_HI_STACK) || (hook &&
 		    (hook->hk_flags & HK_HI_STACK)))))
 			queue = 1;
-#endif
 	}
 
 	if (queue) {
diff --git a/sys/riscv/include/proc.h b/sys/riscv/include/proc.h
index 1c6c8d2919b..e4ca08574be 100644
--- a/sys/riscv/include/proc.h
+++ b/sys/riscv/include/proc.h
@@ -53,4 +53,15 @@ struct syscall_args {
 	register_t args[MAXARGS];
 };
 
+#ifdef _KERNEL
+#include <machine/pcb.h>
+
+/* Get the current kernel thread stack usage. */
+#define	GET_STACK_USAGE(total, used) do {				\
+	struct thread *td = curthread;					\
+	(total) = td->td_kstack_pages * PAGE_SIZE - sizeof(struct pcb);	\
+	(used) = td->td_kstack + (total) - (vm_offset_t)&td;		\
+} while (0)
+
+#endif  /* _KERNEL */
 #endif /* !_MACHINE_PROC_H_ */