From 86df2b8b562cb83152fc050d1eabd8dbd4302115 Mon Sep 17 00:00:00 2001
From: Teng Qin <qinteng@fb.com>
Date: Mon, 23 Apr 2018 12:36:51 -0700
Subject: [PATCH] Add -c option for profile.py

---
 man/man8/profile.8        | 11 +++++++++--
 tools/profile.py          | 26 +++++++++++++++++++++-----
 tools/profile_example.txt |  9 ++++++---
 3 files changed, 36 insertions(+), 10 deletions(-)

diff --git a/man/man8/profile.8 b/man/man8/profile.8
index fca31fd830f4..f44dd6896d6d 100644
--- a/man/man8/profile.8
+++ b/man/man8/profile.8
@@ -2,7 +2,7 @@
 .SH NAME
 profile \- Profile CPU usage by sampling stack traces. Uses Linux eBPF/bcc.
 .SH SYNOPSIS
-.B profile [\-adfh] [\-p PID] [\-U | \-k] [\-F FREQUENCY]
+.B profile [\-adfh] [\-p PID] [\-U | \-K] [\-F FREQUENCY | \-c COUNT]
 .B [\-\-stack\-storage\-size COUNT] [duration]
 .SH DESCRIPTION
 This is a CPU profiler. It works by taking samples of stack traces at timed
@@ -32,7 +32,10 @@ Trace this process ID only (filtered in-kernel). Without this, all CPUs are
 profiled.
 .TP
 \-F frequency
-Frequency to sample stacks (default 49).
+Frequency to sample stacks.
+.TP
+\-c count
+Sample stacks every one in this many events.
 .TP
 \-f
 Print output in folded stack format.
@@ -67,6 +70,10 @@ Profile at 99 Hertz for 5 seconds only:
 #
 .B profile -F 99 5
 .TP
+Profile 1 in a million events for 5 seconds only:
+#
+.B profile -c 1000000 5
+.TP
 Profile PID 181 only:
 #
 .B profile -p 181
diff --git a/tools/profile.py b/tools/profile.py
index e804fb8e2620..1b26ce778ae5 100755
--- a/tools/profile.py
+++ b/tools/profile.py
@@ -63,6 +63,7 @@ def positive_nonzero_int(val):
 examples = """examples:
     ./profile             # profile stack traces at 49 Hertz until Ctrl-C
     ./profile -F 99       # profile stack traces at 99 Hertz
+    ./profile -c 1000000  # profile stack traces every 1 in a million events
     ./profile 5           # profile at 49 Hertz for 5 seconds only
     ./profile -f 5        # output in folded format for flame graphs
     ./profile -p 185      # only profile threads for PID 185
@@ -82,8 +83,11 @@ def positive_nonzero_int(val):
     help="show stacks from user space only (no kernel space stacks)")
 stack_group.add_argument("-K", "--kernel-stacks-only", action="store_true",
     help="show stacks from kernel space only (no user space stacks)")
-parser.add_argument("-F", "--frequency", type=positive_int, default=49,
-    help="sample frequency, Hertz (default 49)")
+sample_group = parser.add_mutually_exclusive_group()
+sample_group.add_argument("-F", "--frequency", type=positive_int,
+    help="sample frequency, Hertz")
+sample_group.add_argument("-c", "--count", type=positive_int,
+    help="sample period, number of events")
 parser.add_argument("-d", "--delimited", action="store_true",
     help="insert delimiter between kernel/user stacks")
 parser.add_argument("-a", "--annotations", action="store_true",
@@ -214,10 +218,22 @@ def positive_nonzero_int(val):
 bpf_text = bpf_text.replace('USER_STACK_GET', user_stack_get)
 bpf_text = bpf_text.replace('KERNEL_STACK_GET', kernel_stack_get)
 
+sample_freq = 0
+sample_period = 0
+if args.frequency:
+    sample_freq = args.frequency
+elif args.count:
+    sample_period = args.count
+else:
+    # If user didn't specify anything, use default 49Hz sampling
+    sample_freq = 49
+sample_context = "%s%d %s" % (("", sample_freq, "Hertz") if sample_freq
+                         else ("every ", sample_period, "events"))
+
 # header
 if not args.folded:
-    print("Sampling at %d Hertz of %s by %s stack" %
-        (args.frequency, thread_context, stack_context), end="")
+    print("Sampling at %s of %s by %s stack" %
+        (sample_context, thread_context, stack_context), end="")
     if duration < 99999999:
         print(" for %d secs." % duration)
     else:
@@ -232,7 +248,7 @@ def positive_nonzero_int(val):
 b = BPF(text=bpf_text)
 b.attach_perf_event(ev_type=PerfType.SOFTWARE,
     ev_config=PerfSWConfig.CPU_CLOCK, fn_name="do_perf_event",
-    sample_period=0, sample_freq=args.frequency)
+    sample_period=sample_period, sample_freq=sample_freq)
 
 # signal handler
 def signal_ignore(signal, frame):
diff --git a/tools/profile_example.txt b/tools/profile_example.txt
index 25f985412c41..efc648c2fd5f 100644
--- a/tools/profile_example.txt
+++ b/tools/profile_example.txt
@@ -704,8 +704,8 @@ Run ./profile -h to see the default.
 USAGE message:
 
 # ./profile -h
-usage: profile [-h] [-p PID] [-U | -K] [-F FREQUENCY] [-d] [-a] [-f]
-                  [--stack-storage-size STACK_STORAGE_SIZE]
+usage: profile [-h] [-p PID] [-U | -K] [-F FREQUENCY | -c COUNT] [-d] [-a]
+                  [-f] [--stack-storage-size STACK_STORAGE_SIZE]
                   [duration]
 
 Profile CPU stack traces at a timed interval
@@ -723,7 +723,9 @@ optional arguments:
                         show stacks from kernel space only (no user space
                         stacks)
   -F FREQUENCY, --frequency FREQUENCY
-                        sample frequency, Hertz (default 49)
+                        sample frequency, Hertz
+  -c COUNT, --count COUNT
+                        sample period, number of events
   -d, --delimited       insert delimiter between kernel/user stacks
   -a, --annotations     add _[k] annotations to kernel frames
   -f, --folded          output folded format, one line per stack (for flame
@@ -735,6 +737,7 @@ optional arguments:
 examples:
     ./profile             # profile stack traces at 49 Hertz until Ctrl-C
     ./profile -F 99       # profile stack traces at 99 Hertz
+    ./profile -c 1000000  # profile stack traces every 1 in a million events
     ./profile 5           # profile at 49 Hertz for 5 seconds only
     ./profile -f 5        # output in folded format for flame graphs
     ./profile -p 185      # only profile threads for PID 185