tracing: Add support for multiple hist triggers per event

Allow users to define any number of hist triggers per trace event.
Any number of hist triggers may be added for a given event, which may
differ by key, value, or filter.

Reading the event's 'hist' file will display the output of all the
hist triggers defined on an event concatenated in the order they were
defined.

Link: http://lkml.kernel.org/r/48a0c8dd34c344571de880fb35e211c6d9a28961.1457029949.git.tom.zanussi@linux.intel.com

Signed-off-by: Tom Zanussi <[email protected]>
Tested-by: Masami Hiramatsu <[email protected]>
Reviewed-by: Namhyung Kim <[email protected]>
Signed-off-by: Steven Rostedt <[email protected]>

Author: tzanussi

Documentation/trace/events.txt

@@ -550,12 +550,14 @@ The following commands are supported:
 
   'hist' triggers add a 'hist' file to each event's subdirectory.
   Reading the 'hist' file for the event will dump the hash table in
-  its entirety to stdout.  Each printed hash table entry is a simple
-  list of the keys and values comprising the entry; keys are printed
-  first and are delineated by curly braces, and are followed by the
-  set of value fields for the entry.  By default, numeric fields are
-  displayed as base-10 integers.  This can be modified by appending
-  any of the following modifiers to the field name:
+  its entirety to stdout.  If there are multiple hist triggers
+  attached to an event, there will be a table for each trigger in the
+  output.  Each printed hash table entry is a simple list of the keys
+  and values comprising the entry; keys are printed first and are
+  delineated by curly braces, and are followed by the set of value
+  fields for the entry.  By default, numeric fields are displayed as
+  base-10 integers.  This can be modified by appending any of the
+  following modifiers to the field name:
 
         .hex        display a number as a hex value
 	.sym        display an address as a symbol
@@ -1667,3 +1669,143 @@ The following commands are supported:
     .
     .
     .
+
+  The following example demonstrates how multiple hist triggers can be
+  attached to a given event.  This capability can be useful for
+  creating a set of different summaries derived from the same set of
+  events, or for comparing the effects of different filters, among
+  other things.
+
+    # echo 'hist:keys=skbaddr.hex:vals=len if len < 0' >> \
+           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+    # echo 'hist:keys=skbaddr.hex:vals=len if len > 4096' >> \
+           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+    # echo 'hist:keys=skbaddr.hex:vals=len if len == 256' >> \
+           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+    # echo 'hist:keys=skbaddr.hex:vals=len' >> \
+           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+    # echo 'hist:keys=len:vals=common_preempt_count' >> \
+           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+
+  The above set of commands create four triggers differing only in
+  their filters, along with a completely different though fairly
+  nonsensical trigger.  Note that in order to append multiple hist
+  triggers to the same file, you should use the '>>' operator to
+  append them ('>' will also add the new hist trigger, but will remove
+  any existing hist triggers beforehand).
+
+  Displaying the contents of the 'hist' file for the event shows the
+  contents of all five histograms:
+
+    # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
+
+    # event histogram
+    #
+    # trigger info: hist:keys=len:vals=hitcount,common_preempt_count:sort=hitcount:size=2048 [active]
+    #
+
+    { len:        176 } hitcount:          1  common_preempt_count:          0
+    { len:        223 } hitcount:          1  common_preempt_count:          0
+    { len:       4854 } hitcount:          1  common_preempt_count:          0
+    { len:        395 } hitcount:          1  common_preempt_count:          0
+    { len:        177 } hitcount:          1  common_preempt_count:          0
+    { len:        446 } hitcount:          1  common_preempt_count:          0
+    { len:       1601 } hitcount:          1  common_preempt_count:          0
+    .
+    .
+    .
+    { len:       1280 } hitcount:         66  common_preempt_count:          0
+    { len:        116 } hitcount:         81  common_preempt_count:         40
+    { len:        708 } hitcount:        112  common_preempt_count:          0
+    { len:         46 } hitcount:        221  common_preempt_count:          0
+    { len:       1264 } hitcount:        458  common_preempt_count:          0
+
+    Totals:
+        Hits: 1428
+        Entries: 147
+        Dropped: 0
+
+
+    # event histogram
+    #
+    # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
+    #
+
+    { skbaddr: ffff8800baee5e00 } hitcount:          1  len:        130
+    { skbaddr: ffff88005f3d5600 } hitcount:          1  len:       1280
+    { skbaddr: ffff88005f3d4900 } hitcount:          1  len:       1280
+    { skbaddr: ffff88009fed6300 } hitcount:          1  len:        115
+    { skbaddr: ffff88009fe0ad00 } hitcount:          1  len:        115
+    { skbaddr: ffff88008cdb1900 } hitcount:          1  len:         46
+    { skbaddr: ffff880064b5ef00 } hitcount:          1  len:        118
+    { skbaddr: ffff880044e3c700 } hitcount:          1  len:         60
+    { skbaddr: ffff880100065900 } hitcount:          1  len:         46
+    { skbaddr: ffff8800d46bd500 } hitcount:          1  len:        116
+    { skbaddr: ffff88005f3d5f00 } hitcount:          1  len:       1280
+    { skbaddr: ffff880100064700 } hitcount:          1  len:        365
+    { skbaddr: ffff8800badb6f00 } hitcount:          1  len:         60
+    .
+    .
+    .
+    { skbaddr: ffff88009fe0be00 } hitcount:         27  len:      24677
+    { skbaddr: ffff88009fe0a400 } hitcount:         27  len:      23052
+    { skbaddr: ffff88009fe0b700 } hitcount:         31  len:      25589
+    { skbaddr: ffff88009fe0b600 } hitcount:         32  len:      27326
+    { skbaddr: ffff88006a462800 } hitcount:         68  len:      71678
+    { skbaddr: ffff88006a463700 } hitcount:         70  len:      72678
+    { skbaddr: ffff88006a462b00 } hitcount:         71  len:      77589
+    { skbaddr: ffff88006a463600 } hitcount:         73  len:      71307
+    { skbaddr: ffff88006a462200 } hitcount:         81  len:      81032
+
+    Totals:
+        Hits: 1451
+        Entries: 318
+        Dropped: 0
+
+
+    # event histogram
+    #
+    # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len == 256 [active]
+    #
+
+
+    Totals:
+        Hits: 0
+        Entries: 0
+        Dropped: 0
+
+
+    # event histogram
+    #
+    # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len > 4096 [active]
+    #
+
+    { skbaddr: ffff88009fd2c300 } hitcount:          1  len:       7212
+    { skbaddr: ffff8800d2bcce00 } hitcount:          1  len:       7212
+    { skbaddr: ffff8800d2bcd700 } hitcount:          1  len:       7212
+    { skbaddr: ffff8800d2bcda00 } hitcount:          1  len:      21492
+    { skbaddr: ffff8800ae2e2d00 } hitcount:          1  len:       7212
+    { skbaddr: ffff8800d2bcdb00 } hitcount:          1  len:       7212
+    { skbaddr: ffff88006a4df500 } hitcount:          1  len:       4854
+    { skbaddr: ffff88008ce47b00 } hitcount:          1  len:      18636
+    { skbaddr: ffff8800ae2e2200 } hitcount:          1  len:      12924
+    { skbaddr: ffff88005f3e1000 } hitcount:          1  len:       4356
+    { skbaddr: ffff8800d2bcdc00 } hitcount:          2  len:      24420
+    { skbaddr: ffff8800d2bcc200 } hitcount:          2  len:      12996
+
+    Totals:
+        Hits: 14
+        Entries: 12
+        Dropped: 0
+
+
+    # event histogram
+    #
+    # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len < 0 [active]
+    #
+
+
+    Totals:
+        Hits: 0
+        Entries: 0
+        Dropped: 0

kernel/trace/trace.c

@@ -3856,9 +3856,11 @@ static const char readme_msg[] =
 	"\t    sort field.  The 'size' parameter can be used to specify more\n"
 	"\t    or fewer than the default 2048 entries for the hashtable size.\n\n"
 	"\t    Reading the 'hist' file for the event will dump the hash\n"
-	"\t    table in its entirety to stdout.  The default format used to\n"
-	"\t    display a given field can be modified by appending any of the\n"
-	"\t    following modifiers to the field name, as applicable:\n\n"
+	"\t    table in its entirety to stdout.  If there are multiple hist\n"
+	"\t    triggers attached to an event, there will be a table for each\n"
+	"\t    trigger in the output.  The default format used to display a\n"
+	"\t    given field can be modified by appending any of the following\n"
+	"\t    modifiers to the field name, as applicable:\n\n"
 	"\t            .hex        display a number as a hex value\n"
 	"\t            .sym        display an address as a symbol\n"
 	"\t            .sym-offset display an address as a symbol and offset\n"