Add tracepoints for taskq entry lifetime events

This adds some new DTRACE_PROBE* endpoints so that we can observe taskq
latencies on a system. Additionally, a new "taskqlatency.bt" script is
added to do this observation via "bpftrace". Lastly, a "zfs-trace.sh"
script is added to wrap "bpftrace" with the proper options required to
run and use "taskqlatency.bt".

For example, with these changes in place, a user can run the following:

    $ cd ./contrib/bpftrace
    $ sudo ./zfs-trace.sh taskqlatency.bt
    Attaching 6 probes...
    ^C

Here's some example output, showing latency information for time spent
executing the taskq entry's function:

    @exec_lat_us[dp_sync_taskq, userquota_updates_task]:
    [2, 4)                 5 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
    [4, 8)                 0 |                                                    |
    [8, 16)                1 |@@@@@@@@@@                                          |
    [16, 32)               2 |@@@@@@@@@@@@@@@@@@@@                                |

    @exec_lat_us[z_wr_int_h, zio_execute]:
    [8, 16)               16 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
    [16, 32)               2 |@@@@@@                                              |

    @exec_lat_us[z_wr_iss_h, zio_execute]:
    [16, 32)               4 |@@@@@@@@@@@@@@@@                                    |
    [32, 64)              13 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
    [64, 128)              1 |@@@@                                                |

    @exec_lat_us[z_ioctl_int, zio_execute]:
    [2, 4)                 1 |@@@@                                                |
    [4, 8)                11 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
    [8, 16)                8 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@               |

    @exec_lat_us[dp_sync_taskq, sync_dnodes_task]:
    [2, 4)                 1 |@@@@@@                                              |
    [4, 8)                 7 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@       |
    [8, 16)                8 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
    [16, 32)               2 |@@@@@@@@@@@@@                                       |
    [32, 64)               4 |@@@@@@@@@@@@@@@@@@@@@@@@@@                          |
    [64, 128)              1 |@@@@@@                                              |
    [128, 256)             0 |                                                    |
    [256, 512)             1 |@@@@@@

Here's some example output, showing latency information for time spent
waiting on the taskq, prior to starting execution of entry's function:

    @queue_lat_us[dp_sync_taskq]:
    [2, 4)                 1 |@@@@                                                |
    [4, 8)                 7 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@                      |
    [8, 16)                2 |@@@@@@@@                                            |
    [16, 32)               3 |@@@@@@@@@@@@@                                       |
    [32, 64)              12 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
    [64, 128)              6 |@@@@@@@@@@@@@@@@@@@@@@@@@@                          |
    [128, 256)             0 |                                                    |
    [256, 512)             1 |@@@@                                                |

    @queue_lat_us[z_wr_iss]:
    [4, 8)                 4 |@@@@                                                |
    [8, 16)               13 |@@@@@@@@@@@@@@@                                     |
    [16, 32)               6 |@@@@@@@                                             |
    [32, 64)               2 |@@                                                  |
    [64, 128)             12 |@@@@@@@@@@@@@@                                      |
    [128, 256)            15 |@@@@@@@@@@@@@@@@@@                                  |
    [256, 512)            33 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@             |
    [512, 1K)             27 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@                    |
    [1K, 2K)               7 |@@@@@@@@                                            |
    [2K, 4K)              14 |@@@@@@@@@@@@@@@@                                    |
    [4K, 8K)              14 |@@@@@@@@@@@@@@@@                                    |
    [8K, 16K)             23 |@@@@@@@@@@@@@@@@@@@@@@@@@@@                         |
    [16K, 32K)            43 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|

    @queue_lat_us[z_wr_int]:
    [2, 4)                10 |@@@@@                                               |
    [4, 8)                71 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@           |
    [8, 16)               88 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
    [16, 32)              50 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@                       |
    [32, 64)              65 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@              |
    [64, 128)             43 |@@@@@@@@@@@@@@@@@@@@@@@@@                           |
    [128, 256)            19 |@@@@@@@@@@@                                         |
    [256, 512)             3 |@                                                   |
    [512, 1K)              1 |                                                    |

Reviewed by: Brad Lewis <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Prakash Surya <[email protected]>
Closes #9525

10 files changed, 181 insertions, 6 deletions

diff --git a/configure.ac b/configure.ac
index 5bcf72bbe..723407558 100644
--- a/configure.ac
+++ b/configure.ac
@@ -86,6 +86,7 @@ AC_CONFIG_FILES([
 	cmd/zvol_wait/Makefile
 	contrib/Makefile
 	contrib/bash_completion.d/Makefile
+	contrib/bpftrace/Makefile
 	contrib/dracut/02zfsexpandknowledge/Makefile
 	contrib/dracut/90zfs/Makefile
 	contrib/dracut/Makefile
diff --git a/contrib/Makefile.am b/contrib/Makefile.am
index 9a82f82ee..9f34fd835 100644
--- a/contrib/Makefile.am
+++ b/contrib/Makefile.am
@@ -1,2 +1,2 @@
-SUBDIRS = bash_completion.d dracut initramfs pyzfs zcp
-DIST_SUBDIRS = bash_completion.d dracut initramfs pyzfs zcp
+SUBDIRS = bash_completion.d bpftrace dracut initramfs pyzfs zcp
+DIST_SUBDIRS = bash_completion.d bpftrace dracut initramfs pyzfs zcp
diff --git a/contrib/bpftrace/Makefile.am b/contrib/bpftrace/Makefile.am
new file mode 100644
index 000000000..c4359e6c8
--- /dev/null
+++ b/contrib/bpftrace/Makefile.am
@@ -0,0 +1,3 @@
+EXTRA_DIST = \
+	$(top_srcdir)/contrib/bpftrace/taskqlatency.bt \
+	$(top_srcdir)/contrib/bpftrace/zfs-trace.sh
diff --git a/contrib/bpftrace/taskqlatency.bt b/contrib/bpftrace/taskqlatency.bt
new file mode 100644
index 000000000..598f9882b
--- /dev/null
+++ b/contrib/bpftrace/taskqlatency.bt
@@ -0,0 +1,54 @@
+#include <sys/taskq.h>
+
+kprobe:trace_zfs_taskq_ent__birth
+{
+        $tqent = (struct taskq_ent *)arg0;
+
+        $tqent_id = $tqent->tqent_id;
+        $tq_name = str($tqent->tqent_taskq->tq_name);
+
+        @birth[$tq_name, $tqent_id] = nsecs;
+}
+
+kprobe:trace_zfs_taskq_ent__start
+{
+        $tqent = (struct taskq_ent *)arg0;
+
+        @tqent_id[tid] = $tqent->tqent_id;
+        @tq_name[tid] = str($tqent->tqent_taskq->tq_name);
+
+        @start[@tq_name[tid], @tqent_id[tid]] = nsecs;
+}
+
+kprobe:trace_zfs_taskq_ent__start
+/ @birth[@tq_name[tid], @tqent_id[tid]] /
+{
+        @queue_lat_us[@tq_name[tid]] =
+                hist((nsecs - @birth[@tq_name[tid], @tqent_id[tid]])/1000);
+        delete(@birth[@tq_name[tid], @tqent_id[tid]]);
+}
+
+kprobe:trace_zfs_taskq_ent__finish
+/ @start[@tq_name[tid], @tqent_id[tid]] /
+{
+        $tqent = (struct taskq_ent *)arg0;
+
+        @exec_lat_us[@tq_name[tid], ksym($tqent->tqent_func)] =
+                hist((nsecs - @start[@tq_name[tid], @tqent_id[tid]])/1000);
+        delete(@start[@tq_name[tid], @tqent_id[tid]]);
+}
+
+kprobe:trace_zfs_taskq_ent__finish
+{
+        delete(@tq_name[tid]);
+        delete(@tqent_id[tid]);
+}
+
+END
+{
+        clear(@birth);
+        clear(@start);
+
+        clear(@tq_name);
+        clear(@tqent_id);
+}
diff --git a/contrib/bpftrace/zfs-trace.sh b/contrib/bpftrace/zfs-trace.sh
new file mode 100755
index 000000000..13230b78c
--- /dev/null
+++ b/contrib/bpftrace/zfs-trace.sh
@@ -0,0 +1,10 @@
+#!/bin/sh
+
+ZVER=$(cat /sys/module/zfs/version | cut -f 1 -d '-')
+KVER=$(uname -r)
+
+bpftrace \
+	--include "/usr/src/zfs-$ZVER/$KVER/zfs_config.h" \
+	-I "/usr/src/zfs-$ZVER/include" \
+	-I "/usr/src/zfs-$ZVER/include/spl" \
+	"$@"
diff --git a/include/os/linux/spl/sys/Makefile.am b/include/os/linux/spl/sys/Makefile.am
index 251542118..e3df4edae 100644
--- a/include/os/linux/spl/sys/Makefile.am
+++ b/include/os/linux/spl/sys/Makefile.am
@@ -46,6 +46,7 @@ KERNEL_H = \
 	$(top_srcdir)/include/os/linux/spl/sys/timer.h \
 	$(top_srcdir)/include/os/linux/spl/sys/trace.h \
 	$(top_srcdir)/include/os/linux/spl/sys/trace_spl.h \
+	$(top_srcdir)/include/os/linux/spl/sys/trace_taskq.h \
 	$(top_srcdir)/include/os/linux/spl/sys/tsd.h \
 	$(top_srcdir)/include/os/linux/spl/sys/types32.h \
 	$(top_srcdir)/include/os/linux/spl/sys/types.h \
diff --git a/include/os/linux/spl/sys/trace_spl.h b/include/os/linux/spl/sys/trace_spl.h
index 6b50d546b..bffd91d91 100644
--- a/include/os/linux/spl/sys/trace_spl.h
+++ b/include/os/linux/spl/sys/trace_spl.h
@@ -22,6 +22,9 @@
 #ifndef _OS_LINUX_SPL_TRACE_H
 #define	_OS_LINUX_SPL_TRACE_H
 
+#include <sys/taskq.h>
+
 #include <sys/trace.h>
+#include <sys/trace_taskq.h>
 
 #endif
diff --git a/include/os/linux/spl/sys/trace_taskq.h b/include/os/linux/spl/sys/trace_taskq.h
new file mode 100644
index 000000000..dbbb3c4c7
--- /dev/null
+++ b/include/os/linux/spl/sys/trace_taskq.h
@@ -0,0 +1,89 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+
+#if defined(_KERNEL)
+#if defined(HAVE_DECLARE_EVENT_CLASS)
+
+#undef TRACE_SYSTEM
+#define	TRACE_SYSTEM zfs
+
+#undef TRACE_SYSTEM_VAR
+#define	TRACE_SYSTEM_VAR zfs_taskq
+
+#if !defined(_TRACE_TASKQ_H) || defined(TRACE_HEADER_MULTI_READ)
+#define	_TRACE_TASKQ_H
+
+#include <linux/tracepoint.h>
+#include <sys/types.h>
+
+/*
+ * Generic support for single argument tracepoints of the form:
+ *
+ * DTRACE_PROBE1(...,
+ *     taskq_ent_t *, ...);
+ */
+/* BEGIN CSTYLED */
+DECLARE_EVENT_CLASS(zfs_taskq_ent_class,
+	TP_PROTO(taskq_ent_t *taskq_ent),
+	TP_ARGS(taskq_ent),
+	TP_STRUCT__entry(
+	    __field(taskq_ent_t *,	taskq_ent)
+	),
+	TP_fast_assign(
+	    __entry->taskq_ent	= taskq_ent;
+	),
+	TP_printk("taskq_ent %p", __entry->taskq_ent)
+);
+/* END CSTYLED */
+
+/* BEGIN CSTYLED */
+#define DEFINE_TASKQ_EVENT(name) \
+DEFINE_EVENT(zfs_taskq_ent_class, name, \
+	TP_PROTO(taskq_ent_t *taskq_ent), \
+	TP_ARGS(taskq_ent))
+/* END CSTYLED */
+DEFINE_TASKQ_EVENT(zfs_taskq_ent__birth);
+DEFINE_TASKQ_EVENT(zfs_taskq_ent__start);
+DEFINE_TASKQ_EVENT(zfs_taskq_ent__finish);
+
+#endif /* _TRACE_TASKQ_H */
+
+#undef TRACE_INCLUDE_PATH
+#undef TRACE_INCLUDE_FILE
+#define	TRACE_INCLUDE_PATH sys
+#define	TRACE_INCLUDE_FILE trace_taskq
+#include <trace/define_trace.h>
+
+#else
+
+/*
+ * When tracepoints are not available, a DEFINE_DTRACE_PROBE* macro is
+ * needed for each DTRACE_PROBE.  These will be used to generate stub
+ * tracing functions and prototypes for those functions.  See
+ * include/os/linux/spl/sys/trace.h.
+ */
+
+DEFINE_DTRACE_PROBE1(taskq_ent__birth);
+DEFINE_DTRACE_PROBE1(taskq_ent__start);
+DEFINE_DTRACE_PROBE1(taskq_ent__finish);
+
+#endif /* HAVE_DECLARE_EVENT_CLASS */
+#endif /* _KERNEL */
diff --git a/module/os/linux/spl/spl-taskq.c b/module/os/linux/spl/spl-taskq.c
index 8910c109e..a01c4b475 100644
--- a/module/os/linux/spl/spl-taskq.c
+++ b/module/os/linux/spl/spl-taskq.c
@@ -28,6 +28,7 @@
 #include <sys/taskq.h>
 #include <sys/kmem.h>
 #include <sys/tsd.h>
+#include <sys/trace_spl.h>
 
 int spl_taskq_thread_bind = 0;
 module_param(spl_taskq_thread_bind, int, 0644);
@@ -223,6 +224,8 @@ task_expire_impl(taskq_ent_t *t)
 	}
 
 	t->tqent_birth = jiffies;
+	DTRACE_PROBE1(taskq_ent__birth, taskq_ent_t *, t);
+
 	/*
 	 * The priority list must be maintained in strict task id order
 	 * from lowest to highest for lowest_id to be easily calculable.
@@ -593,7 +596,9 @@ taskq_dispatch(taskq_t *tq, task_func_t func, void *arg, uint_t flags)
 	t->tqent_taskq = tq;
 	t->tqent_timer.function = NULL;
 	t->tqent_timer.expires = 0;
+
 	t->tqent_birth = jiffies;
+	DTRACE_PROBE1(taskq_ent__birth, taskq_ent_t *, t);
 
 	ASSERT(!(t->tqent_flags & TQENT_FLAG_PREALLOC));
 
@@ -706,7 +711,9 @@ taskq_dispatch_ent(taskq_t *tq, task_func_t func, void *arg, uint_t flags,
 	t->tqent_func = func;
 	t->tqent_arg = arg;
 	t->tqent_taskq = tq;
+
 	t->tqent_birth = jiffies;
+	DTRACE_PROBE1(taskq_ent__birth, taskq_ent_t *, t);
 
 	spin_unlock(&t->tqent_lock);
 
@@ -906,15 +913,15 @@ taskq_thread(void *args)
 			 * tqent_flags here.
 			 *
 			 * Also use an on stack taskq_ent_t for tqt_task
-			 * assignment in this case. We only populate the two
-			 * fields used by the only user in taskq proc file.
+			 * assignment in this case; we want to make sure
+			 * to duplicate all fields, so the values are
+			 * correct when it's accessed via DTRACE_PROBE*.
 			 */
 			tqt->tqt_id = t->tqent_id;
 			tqt->tqt_flags = t->tqent_flags;
 
 			if (t->tqent_flags & TQENT_FLAG_PREALLOC) {
-				dup_task.tqent_func = t->tqent_func;
-				dup_task.tqent_arg = t->tqent_arg;
+				dup_task = *t;
 				t = &dup_task;
 			}
 			tqt->tqt_task = t;
@@ -923,9 +930,13 @@ taskq_thread(void *args)
 			tq->tq_nactive++;
 			spin_unlock_irqrestore(&tq->tq_lock, flags);
 
+			DTRACE_PROBE1(taskq_ent__start, taskq_ent_t *, t);
+
 			/* Perform the requested task */
 			t->tqent_func(t->tqent_arg);
 
+			DTRACE_PROBE1(taskq_ent__finish, taskq_ent_t *, t);
+
 			spin_lock_irqsave_nested(&tq->tq_lock, flags,
 			    tq->tq_lock_class);
 			tq->tq_nactive--;
diff --git a/module/os/linux/spl/spl-trace.c b/module/os/linux/spl/spl-trace.c
index 6415f9a91..7912a3812 100644
--- a/module/os/linux/spl/spl-trace.c
+++ b/module/os/linux/spl/spl-trace.c
@@ -24,7 +24,10 @@
  * source file, so this dummy file exists for that purpose.
  */
 
+#include <sys/taskq.h>
+
 #ifdef _KERNEL
 #define	CREATE_TRACE_POINTS
 #include <sys/trace.h>
+#include <sys/trace_taskq.h>
 #endif