tracing/events: convert block trace points to TRACE_EVENT()

TRACE_EVENT is a more generic way to define tracepoints. Doing so adds
these new capabilities to this tracepoint:

  - zero-copy and per-cpu splice() tracing
  - binary tracing without printf overhead
  - structured logging records exposed under /debug/tracing/events
  - trace events embedded in function tracer output and other plugins
  - user-defined, per tracepoint filter expressions
  ...

Cons:

  - no dev_t info for the output of plug, unplug_timer and unplug_io events.
    no dev_t info for getrq and sleeprq events if bio == NULL.
    no dev_t info for rq_abort,...,rq_requeue events if rq->rq_disk == NULL.

    This is mainly because we can't get the deivce from a request queue.
    But this may change in the future.

  - A packet command is converted to a string in TP_assign, not TP_print.
    While blktrace do the convertion just before output.

    Since pc requests should be rather rare, this is not a big issue.

  - In blktrace, an event can have 2 different print formats, but a TRACE_EVENT
    has a unique format, which means we have some unused data in a trace entry.

    The overhead is minimized by using __dynamic_array() instead of __array().

I've benchmarked the ioctl blktrace vs the splice based TRACE_EVENT tracing:

      dd                   dd + ioctl blktrace       dd + TRACE_EVENT (splice)
1     7.36s, 42.7 MB/s     7.50s, 42.0 MB/s          7.41s, 42.5 MB/s
2     7.43s, 42.3 MB/s     7.48s, 42.1 MB/s          7.43s, 42.4 MB/s
3     7.38s, 42.6 MB/s     7.45s, 42.2 MB/s          7.41s, 42.5 MB/s

So the overhead of tracing is very small, and no regression when using
those trace events vs blktrace.

And the binary output of TRACE_EVENT is much smaller than blktrace:

 # ls -l -h
 -rw-r--r-- 1 root root 8.8M 06-09 13:24 sda.blktrace.0
 -rw-r--r-- 1 root root 195K 06-09 13:24 sda.blktrace.1
 -rw-r--r-- 1 root root 2.7M 06-09 13:25 trace_splice.out

Following are some comparisons between TRACE_EVENT and blktrace:

plug:
  kjournald-480   [000]   303.084981: block_plug: [kjournald]
  kjournald-480   [000]   303.084981:   8,0    P   N [kjournald]

unplug_io:
  kblockd/0-118   [000]   300.052973: block_unplug_io: [kblockd/0] 1
  kblockd/0-118   [000]   300.052974:   8,0    U   N [kblockd/0] 1

remap:
  kjournald-480   [000]   303.085042: block_remap: 8,0 W 102736992 + 8 <- (8,8) 33384
  kjournald-480   [000]   303.085043:   8,0    A   W 102736992 + 8 <- (8,8) 33384

bio_backmerge:
  kjournald-480   [000]   303.085086: block_bio_backmerge: 8,0 W 102737032 + 8 [kjournald]
  kjournald-480   [000]   303.085086:   8,0    M   W 102737032 + 8 [kjournald]

getrq:
  kjournald-480   [000]   303.084974: block_getrq: 8,0 W 102736984 + 8 [kjournald]
  kjournald-480   [000]   303.084975:   8,0    G   W 102736984 + 8 [kjournald]

  bash-2066  [001]  1072.953770:   8,0    G   N [bash]
  bash-2066  [001]  1072.953773: block_getrq: 0,0 N 0 + 0 [bash]

rq_complete:
  konsole-2065  [001]   300.053184: block_rq_complete: 8,0 W () 103669040 + 16 [0]
  konsole-2065  [001]   300.053191:   8,0    C   W 103669040 + 16 [0]

  ksoftirqd/1-7   [001]  1072.953811:   8,0    C   N (5a 00 08 00 00 00 00 00 24 00) [0]
  ksoftirqd/1-7   [001]  1072.953813: block_rq_complete: 0,0 N (5a 00 08 00 00 00 00 00 24 00) 0 + 0 [0]

rq_insert:
  kjournald-480   [000]   303.084985: block_rq_insert: 8,0 W 0 () 102736984 + 8 [kjournald]
  kjournald-480   [000]   303.084986:   8,0    I   W 102736984 + 8 [kjournald]

Changelog from v2 -> v3:

- use the newly introduced __dynamic_array().

Changelog from v1 -> v2:

- use __string() instead of __array() to minimize the memory required
  to store hex dump of rq->cmd().

- support large pc requests.

- add missing blk_fill_rwbs_rq() in block_rq_requeue TRACE_EVENT.

- some cleanups.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4A2DF669.5070905@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 81 insertions, 2 deletions

diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index 06b85850fab4..844164dca90a 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -45,7 +45,10 @@ obj-$(CONFIG_HW_BRANCH_TRACER) += trace_hw_branches.o
 obj-$(CONFIG_POWER_TRACER) += trace_power.o
 obj-$(CONFIG_KMEMTRACE) += kmemtrace.o
 obj-$(CONFIG_WORKQUEUE_TRACER) += trace_workqueue.o
-obj-$(CONFIG_BLK_DEV_IO_TRACE)	+= blktrace.o
+obj-$(CONFIG_BLK_DEV_IO_TRACE) += blktrace.o
+ifeq ($(CONFIG_BLOCK),y)
+obj-$(CONFIG_EVENT_TRACING) += blktrace.o
+endif
 obj-$(CONFIG_EVENT_TRACING) += trace_events.o
 obj-$(CONFIG_EVENT_TRACING) += trace_export.o
 obj-$(CONFIG_FTRACE_SYSCALLS) += trace_syscalls.o
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index e3abf55bc8e5..7bd6a9893c24 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -23,10 +23,14 @@
 #include <linux/mutex.h>
 #include <linux/debugfs.h>
 #include <linux/time.h>
-#include <trace/block.h>
 #include <linux/uaccess.h>
+
+#include <trace/events/block.h>
+
 #include "trace_output.h"
 
+#ifdef CONFIG_BLK_DEV_IO_TRACE
+
 static unsigned int blktrace_seq __read_mostly = 1;
 
 static struct trace_array *blk_tr;
@@ -1658,3 +1662,75 @@ int blk_trace_init_sysfs(struct device *dev)
 	return sysfs_create_group(&dev->kobj, &blk_trace_attr_group);
 }
 
+#endif /* CONFIG_BLK_DEV_IO_TRACE */
+
+#ifdef CONFIG_EVENT_TRACING
+
+void blk_dump_cmd(char *buf, struct request *rq)
+{
+	int i, end;
+	int len = rq->cmd_len;
+	unsigned char *cmd = rq->cmd;
+
+	if (!blk_pc_request(rq)) {
+		buf[0] = '\0';
+		return;
+	}
+
+	for (end = len - 1; end >= 0; end--)
+		if (cmd[end])
+			break;
+	end++;
+
+	for (i = 0; i < len; i++) {
+		buf += sprintf(buf, "%s%02x", i == 0 ? "" : " ", cmd[i]);
+		if (i == end && end != len - 1) {
+			sprintf(buf, " ..");
+			break;
+		}
+	}
+}
+
+void blk_fill_rwbs(char *rwbs, u32 rw, int bytes)
+{
+	int i = 0;
+
+	if (rw & WRITE)
+		rwbs[i++] = 'W';
+	else if (rw & 1 << BIO_RW_DISCARD)
+		rwbs[i++] = 'D';
+	else if (bytes)
+		rwbs[i++] = 'R';
+	else
+		rwbs[i++] = 'N';
+
+	if (rw & 1 << BIO_RW_AHEAD)
+		rwbs[i++] = 'A';
+	if (rw & 1 << BIO_RW_BARRIER)
+		rwbs[i++] = 'B';
+	if (rw & 1 << BIO_RW_SYNCIO)
+		rwbs[i++] = 'S';
+	if (rw & 1 << BIO_RW_META)
+		rwbs[i++] = 'M';
+
+	rwbs[i] = '\0';
+}
+
+void blk_fill_rwbs_rq(char *rwbs, struct request *rq)
+{
+	int rw = rq->cmd_flags & 0x03;
+	int bytes;
+
+	if (blk_discard_rq(rq))
+		rw |= (1 << BIO_RW_DISCARD);
+
+	if (blk_pc_request(rq))
+		bytes = rq->data_len;
+	else
+		bytes = rq->hard_nr_sectors << 9;
+
+	blk_fill_rwbs(rwbs, rw, bytes);
+}
+
+#endif /* CONFIG_EVENT_TRACING */
+