From 5289f6f961557bf504c4ef7009d0e5342f10f65a Mon Sep 17 00:00:00 2001
From: Olivier Certner <olce@FreeBSD.org>
Date: Mon, 30 Jun 2025 16:24:23 +0200
Subject: [PATCH] spa: ZIO_TASKQ_ISSUE: Use symbolic priority

This allows to change the meaning of priority differences in FreeBSD
without requiring code changes in ZFS.

This upstreams commit fd141584cf89d7d2 from FreeBSD src.

Sponsored-by: The FreeBSD Foundation
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Olivier Certner <olce@FreeBSD.org>
Closes #17489
---
 include/os/freebsd/spl/sys/proc.h    |  4 +++-
 include/os/linux/spl/sys/sysmacros.h |  4 +++-
 include/sys/zfs_context.h            |  4 +++-
 module/zfs/spa.c                     | 21 +++------------------
 4 files changed, 12 insertions(+), 21 deletions(-)

diff --git a/include/os/freebsd/spl/sys/proc.h b/include/os/freebsd/spl/sys/proc.h
index a03b815a2..c6bc10d6b 100644
--- a/include/os/freebsd/spl/sys/proc.h
+++ b/include/os/freebsd/spl/sys/proc.h
@@ -45,7 +45,9 @@
 #ifdef _KERNEL
 #define	CPU		curcpu
 #define	minclsyspri	PRIBIO
-#define	defclsyspri minclsyspri
+#define	defclsyspri	minclsyspri
+/* Write issue taskq priority. */
+#define	wtqclsyspri	((PVM + PRIBIO) / 2)
 #define	maxclsyspri	PVM
 #define	max_ncpus	(mp_maxid + 1)
 #define	boot_max_ncpus	(mp_maxid + 1)
diff --git a/include/os/linux/spl/sys/sysmacros.h b/include/os/linux/spl/sys/sysmacros.h
index e932ea72f..db48222b7 100644
--- a/include/os/linux/spl/sys/sysmacros.h
+++ b/include/os/linux/spl/sys/sysmacros.h
@@ -92,8 +92,10 @@
  * Treat shim tasks as SCHED_NORMAL tasks
  */
 #define	minclsyspri			(MAX_PRIO-1)
-#define	maxclsyspri			(MAX_RT_PRIO)
 #define	defclsyspri			(DEFAULT_PRIO)
+/* Write issue taskq priority. */
+#define	wtqclsyspri			(MAX_RT_PRIO + 1)
+#define	maxclsyspri			(MAX_RT_PRIO)
 
 #ifndef NICE_TO_PRIO
 #define	NICE_TO_PRIO(nice)		(MAX_RT_PRIO + (nice) + 20)
diff --git a/include/sys/zfs_context.h b/include/sys/zfs_context.h
index 272b22174..c06443b4b 100644
--- a/include/sys/zfs_context.h
+++ b/include/sys/zfs_context.h
@@ -628,8 +628,10 @@ extern void delay(clock_t ticks);
  * Process priorities as defined by setpriority(2) and getpriority(2).
  */
 #define	minclsyspri	19
-#define	maxclsyspri	-20
 #define	defclsyspri	0
+/* Write issue taskq priority. */
+#define	wtqclsyspri	-19
+#define	maxclsyspri	-20
 
 #define	CPU_SEQID	((uintptr_t)pthread_self() & (max_ncpus - 1))
 #define	CPU_SEQID_UNSTABLE	CPU_SEQID
diff --git a/module/zfs/spa.c b/module/zfs/spa.c
index 01363181b..74a943ef8 100644
--- a/module/zfs/spa.c
+++ b/module/zfs/spa.c
@@ -1231,29 +1231,14 @@ spa_taskqs_init(spa_t *spa, zio_type_t t, zio_taskq_type_t q)
 			    spa->spa_proc, zio_taskq_basedc, flags);
 		} else {
 #endif
-			pri_t pri = maxclsyspri;
 			/*
 			 * The write issue taskq can be extremely CPU
 			 * intensive.  Run it at slightly less important
 			 * priority than the other taskqs.
-			 *
-			 * Under Linux and FreeBSD this means incrementing
-			 * the priority value as opposed to platforms like
-			 * illumos where it should be decremented.
-			 *
-			 * On FreeBSD, if priorities divided by four (RQ_PPQ)
-			 * are equal then a difference between them is
-			 * insignificant.
 			 */
-			if (t == ZIO_TYPE_WRITE && q == ZIO_TASKQ_ISSUE) {
-#if defined(__linux__)
-				pri++;
-#elif defined(__FreeBSD__)
-				pri += 4;
-#else
-#error "unknown OS"
-#endif
-			}
+			const pri_t pri = (t == ZIO_TYPE_WRITE &&
+			    q == ZIO_TASKQ_ISSUE) ?
+			    wtqclsyspri : maxclsyspri;
 			tq = taskq_create_proc(name, value, pri, 50,
 			    INT_MAX, spa->spa_proc, flags);
 #ifdef HAVE_SYSDC