diff --git a/man/man4/zfs.4 b/man/man4/zfs.4
index 0c60a9c8e..d8a62384f 100644
--- a/man/man4/zfs.4
+++ b/man/man4/zfs.4
@@ -2216,6 +2216,16 @@ If
.Sy 0 ,
generate a system-dependent value close to 6 threads per taskq.
.
+.It Sy zio_taskq_read Ns = Ns Sy fixed,1,8 null scale null Pq charp
+Set the queue and thread configuration for the IO read queues.
+This is an advanced debugging parameter.
+Don't change this unless you understand what it does.
+.
+.It Sy zio_taskq_write Ns = Ns Sy batch fixed,1,5 scale fixed,1,5 Pq charp
+Set the queue and thread configuration for the IO write queues.
+This is an advanced debugging parameter.
+Don't change this unless you understand what it does.
+.
.It Sy zvol_inhibit_dev Ns = Ns Sy 0 Ns | Ns 1 Pq uint
Do not create zvol device nodes.
This may slightly improve startup time on
diff --git a/module/zfs/spa.c b/module/zfs/spa.c
index 5f238e691..ee211ffcf 100644
--- a/module/zfs/spa.c
+++ b/module/zfs/spa.c
@@ -151,7 +151,7 @@ static const char *const zio_taskq_types[ZIO_TASKQ_TYPES] = {
* and interrupt) and then to reserve threads for ZIO_PRIORITY_NOW I/Os that
* need to be handled with minimum delay.
*/
-const zio_taskq_info_t zio_taskqs[ZIO_TYPES][ZIO_TASKQ_TYPES] = {
+static zio_taskq_info_t zio_taskqs[ZIO_TYPES][ZIO_TASKQ_TYPES] = {
/* ISSUE ISSUE_HIGH INTR INTR_HIGH */
{ ZTI_ONE, ZTI_NULL, ZTI_ONE, ZTI_NULL }, /* NULL */
{ ZTI_N(8), ZTI_NULL, ZTI_SCALE, ZTI_NULL }, /* READ */
@@ -1111,6 +1111,292 @@ spa_taskqs_fini(spa_t *spa, zio_type_t t, zio_taskq_type_t q)
tqs->stqs_taskq = NULL;
}
+#ifdef _KERNEL
+/*
+ * The READ and WRITE rows of zio_taskqs are configurable at module load time
+ * by setting zio_taskq_read or zio_taskq_write.
+ *
+ * Example (the defaults for READ and WRITE)
+ * zio_taskq_read='fixed,1,8 null scale null'
+ * zio_taskq_write='batch fixed,1,5 scale fixed,1,5'
+ *
+ * Each sets the entire row at a time.
+ *
+ * 'fixed' is parameterised: fixed,Q,T where Q is number of taskqs, T is number
+ * of threads per taskq.
+ *
+ * 'null' can only be set on the high-priority queues (queue selection for
+ * high-priority queues will fall back to the regular queue if the high-pri
+ * is NULL.
+ */
+static const char *const modes[ZTI_NMODES] = {
+ "fixed", "batch", "scale", "null"
+};
+
+/* Parse the incoming config string. Modifies cfg */
+static int
+spa_taskq_param_set(zio_type_t t, char *cfg)
+{
+ int err = 0;
+
+ zio_taskq_info_t row[ZIO_TASKQ_TYPES] = {{0}};
+
+ char *next = cfg, *tok, *c;
+
+ /*
+ * Parse out each element from the string and fill `row`. The entire
+ * row has to be set at once, so any errors are flagged by just
+ * breaking out of this loop early.
+ */
+ uint_t q;
+ for (q = 0; q < ZIO_TASKQ_TYPES; q++) {
+ /* `next` is the start of the config */
+ if (next == NULL)
+ break;
+
+ /* Eat up leading space */
+ while (isspace(*next))
+ next++;
+ if (*next == '\0')
+ break;
+
+ /* Mode ends at space or end of string */
+ tok = next;
+ next = strchr(tok, ' ');
+ if (next != NULL) *next++ = '\0';
+
+ /* Parameters start after a comma */
+ c = strchr(tok, ',');
+ if (c != NULL) *c++ = '\0';
+
+ /* Match mode string */
+ uint_t mode;
+ for (mode = 0; mode < ZTI_NMODES; mode++)
+ if (strcmp(tok, modes[mode]) == 0)
+ break;
+ if (mode == ZTI_NMODES)
+ break;
+
+ /* Invalid canary */
+ row[q].zti_mode = ZTI_NMODES;
+
+ /* Per-mode setup */
+ switch (mode) {
+
+ /*
+ * FIXED is parameterised: number of queues, and number of
+ * threads per queue.
+ */
+ case ZTI_MODE_FIXED: {
+ /* No parameters? */
+ if (c == NULL || *c == '\0')
+ break;
+
+ /* Find next parameter */
+ tok = c;
+ c = strchr(tok, ',');
+ if (c == NULL)
+ break;
+
+ /* Take digits and convert */
+ unsigned long long nq;
+ if (!(isdigit(*tok)))
+ break;
+ err = ddi_strtoull(tok, &tok, 10, &nq);
+ /* Must succeed and also end at the next param sep */
+ if (err != 0 || tok != c)
+ break;
+
+ /* Move past the comma */
+ tok++;
+ /* Need another number */
+ if (!(isdigit(*tok)))
+ break;
+ /* Remember start to make sure we moved */
+ c = tok;
+
+ /* Take digits */
+ unsigned long long ntpq;
+ err = ddi_strtoull(tok, &tok, 10, &ntpq);
+ /* Must succeed, and moved forward */
+ if (err != 0 || tok == c || *tok != '\0')
+ break;
+
+ /*
+ * sanity; zero queues/threads make no sense, and
+ * 16K is almost certainly more than anyone will ever
+ * need and avoids silly numbers like UINT32_MAX
+ */
+ if (nq == 0 || nq >= 16384 ||
+ ntpq == 0 || ntpq >= 16384)
+ break;
+
+ const zio_taskq_info_t zti = ZTI_P(ntpq, nq);
+ row[q] = zti;
+ break;
+ }
+
+ case ZTI_MODE_BATCH: {
+ const zio_taskq_info_t zti = ZTI_BATCH;
+ row[q] = zti;
+ break;
+ }
+
+ case ZTI_MODE_SCALE: {
+ const zio_taskq_info_t zti = ZTI_SCALE;
+ row[q] = zti;
+ break;
+ }
+
+ case ZTI_MODE_NULL: {
+ /*
+ * Can only null the high-priority queues; the general-
+ * purpose ones have to exist.
+ */
+ if (q != ZIO_TASKQ_ISSUE_HIGH &&
+ q != ZIO_TASKQ_INTERRUPT_HIGH)
+ break;
+
+ const zio_taskq_info_t zti = ZTI_NULL;
+ row[q] = zti;
+ break;
+ }
+
+ default:
+ break;
+ }
+
+ /* Ensure we set a mode */
+ if (row[q].zti_mode == ZTI_NMODES)
+ break;
+ }
+
+ /* Didn't get a full row, fail */
+ if (q < ZIO_TASKQ_TYPES)
+ return (SET_ERROR(EINVAL));
+
+ /* Eat trailing space */
+ if (next != NULL)
+ while (isspace(*next))
+ next++;
+
+ /* If there's anything left over then fail */
+ if (next != NULL && *next != '\0')
+ return (SET_ERROR(EINVAL));
+
+ /* Success! Copy it into the real config */
+ for (q = 0; q < ZIO_TASKQ_TYPES; q++)
+ zio_taskqs[t][q] = row[q];
+
+ return (0);
+}
+
+static int
+spa_taskq_param_get(zio_type_t t, char *buf)
+{
+ int pos = 0;
+
+ /* Build paramater string from live config */
+ const char *sep = "";
+ for (uint_t q = 0; q < ZIO_TASKQ_TYPES; q++) {
+ const zio_taskq_info_t *zti = &zio_taskqs[t][q];
+ if (zti->zti_mode == ZTI_MODE_FIXED)
+ pos += sprintf(&buf[pos], "%s%s,%u,%u", sep,
+ modes[zti->zti_mode], zti->zti_count,
+ zti->zti_value);
+ else
+ pos += sprintf(&buf[pos], "%s%s", sep,
+ modes[zti->zti_mode]);
+ sep = " ";
+ }
+
+ buf[pos++] = '\n';
+ buf[pos] = '\0';
+
+ return (pos);
+}
+
+#ifdef __linux__
+static int
+spa_taskq_read_param_set(const char *val, zfs_kernel_param_t *kp)
+{
+ char *cfg = kmem_strdup(val);
+ int err = spa_taskq_param_set(ZIO_TYPE_READ, cfg);
+ kmem_free(cfg, strlen(val)+1);
+ return (-err);
+}
+static int
+spa_taskq_read_param_get(char *buf, zfs_kernel_param_t *kp)
+{
+ return (spa_taskq_param_get(ZIO_TYPE_READ, buf));
+}
+
+static int
+spa_taskq_write_param_set(const char *val, zfs_kernel_param_t *kp)
+{
+ char *cfg = kmem_strdup(val);
+ int err = spa_taskq_param_set(ZIO_TYPE_WRITE, cfg);
+ kmem_free(cfg, strlen(val)+1);
+ return (-err);
+}
+static int
+spa_taskq_write_param_get(char *buf, zfs_kernel_param_t *kp)
+{
+ return (spa_taskq_param_get(ZIO_TYPE_WRITE, buf));
+}
+#else
+#include <sys/sbuf.h>
+
+/*
+ * On FreeBSD load-time parameters can be set up before malloc() is available,
+ * so we have to do all the parsing work on the stack.
+ */
+#define SPA_TASKQ_PARAM_MAX (128)
+
+static int
+spa_taskq_read_param(ZFS_MODULE_PARAM_ARGS)
+{
+ char buf[SPA_TASKQ_PARAM_MAX];
+ int err = 0;
+
+ if (req->newptr == NULL) {
+ int len = spa_taskq_param_get(ZIO_TYPE_READ, buf);
+ struct sbuf *s = sbuf_new_for_sysctl(NULL, NULL, len+1, req);
+ sbuf_cpy(s, buf);
+ err = sbuf_finish(s);
+ sbuf_delete(s);
+ return (err);
+ }
+
+ err = sysctl_handle_string(oidp, buf, sizeof (buf), req);
+ if (err)
+ return (err);
+ return (spa_taskq_param_set(ZIO_TYPE_READ, buf));
+}
+
+static int
+spa_taskq_write_param(ZFS_MODULE_PARAM_ARGS)
+{
+ char buf[SPA_TASKQ_PARAM_MAX];
+ int err = 0;
+
+ if (req->newptr == NULL) {
+ int len = spa_taskq_param_get(ZIO_TYPE_WRITE, buf);
+ struct sbuf *s = sbuf_new_for_sysctl(NULL, NULL, len+1, req);
+ sbuf_cpy(s, buf);
+ err = sbuf_finish(s);
+ sbuf_delete(s);
+ return (err);
+ }
+
+ err = sysctl_handle_string(oidp, buf, sizeof (buf), req);
+ if (err)
+ return (err);
+ return (spa_taskq_param_set(ZIO_TYPE_WRITE, buf));
+}
+#endif
+#endif /* _KERNEL */
+
/*
* Dispatch a task to the appropriate taskq for the ZFS I/O type and priority.
* Note that a type may have multiple discrete taskqs to avoid lock contention
@@ -10007,4 +10293,13 @@ ZFS_MODULE_PARAM(zfs_livelist_condense, zfs_livelist_condense_, zthr_cancel, INT
ZFS_MODULE_PARAM(zfs_livelist_condense, zfs_livelist_condense_, new_alloc, INT, ZMOD_RW,
"Whether extra ALLOC blkptrs were added to a livelist entry while it "
"was being condensed");
+
+#ifdef _KERNEL
+ZFS_MODULE_VIRTUAL_PARAM_CALL(zfs_zio, zio_, taskq_read,
+ spa_taskq_read_param_set, spa_taskq_read_param_get, ZMOD_RD,
+ "Configure IO queues for read IO");
+ZFS_MODULE_VIRTUAL_PARAM_CALL(zfs_zio, zio_, taskq_write,
+ spa_taskq_write_param_set, spa_taskq_write_param_get, ZMOD_RD,
+ "Configure IO queues for write IO");
+#endif
/* END CSTYLED */