rpms/trace-cmd
5
0
Fork 0
Code Issues Pull Requests Releases Activity
390eb54eab
trace-cmd/trace-cmd-Add-option-to-poll-trace-buffers.patch

175 lines
6.0 KiB
Diff
Raw Blame History

From b206acf0f4bb4a8aff22b14139b6d5fdcb110b77 Mon Sep 17 00:00:00 2001
From: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Date: Wed, 2 Jun 2021 11:08:03 +0200
Subject: [PATCH] trace-cmd: Add option to poll trace buffers
Waiting for data to be available on the trace ring-buffers may trigger
IPIs. This might generate unacceptable trace noise when debugging low
latency or real time systems. So introduce the poll option. When
enabled, it forces trace-cmd to use O_NONBLOCK. The drawback to using it
is that traces will be extracted by busy waiting, which will
unnecessarily hog the CPUs, so only use when really needed.
Link: https://lore.kernel.org/linux-trace-devel/20210602090803.12233-1-nsaenzju@redhat.com
Signed-off-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
Documentation/trace-cmd-record.1.txt | 7 +++++++
trace-cmd.h | 4 +++-
trace-record.c | 9 ++++++++-
trace-recorder.c | 29 +++++++++++++++-------------
trace-usage.c | 1 +
5 files changed, 35 insertions(+), 15 deletions(-)
diff --git a/Documentation/trace-cmd-record.1.txt b/Documentation/trace-cmd-record.1.txt
index 26a8299c..2b3ce636 100644
--- a/Documentation/trace-cmd-record.1.txt
+++ b/Documentation/trace-cmd-record.1.txt
@@ -331,6 +331,13 @@ OPTIONS
executed will not be changed. This is useful if you want to monitor the
output of the command being executed, but not see the output from trace-cmd.
+*--poll*::
+ Waiting for data to be available on the trace ring-buffers may trigger
+ IPIs. This might generate unacceptable trace noise when tracing low latency
+ or real time systems. The poll option forces trace-cmd to use O_NONBLOCK.
+ Traces are extracted by busy waiting, which will hog the CPUs, so only use
+ when really needed.
+
EXAMPLES
--------
diff --git a/trace-cmd.h b/trace-cmd.h
index 75951b5e..4cc9db2a 100644
--- a/trace-cmd.h
+++ b/trace-cmd.h
@@ -279,7 +279,9 @@ int tracecmd_attach_cpu_data_fd(int fd, int cpus, char * const *cpu_data_files);
enum {
TRACECMD_RECORD_NOSPLICE = (1 << 0), /* Use read instead of splice */
TRACECMD_RECORD_SNAPSHOT = (1 << 1), /* extract from snapshot */
- TRACECMD_RECORD_BLOCK = (1 << 2), /* Block on splice write */
+ TRACECMD_RECORD_BLOCK_SPLICE = (1 << 2), /* Block on splice write */
+ TRACECMD_RECORD_NOBRASS = (1 << 3), /* Splice directly without a brass pipe */
+ TRACECMD_RECORD_POLL = (1 << 4), /* Use O_NONBLOCK, poll trace buffers */
};
void tracecmd_free_recorder(struct tracecmd_recorder *recorder);
diff --git a/trace-record.c b/trace-record.c
index ef4c4c87..1872e3c4 100644
--- a/trace-record.c
+++ b/trace-record.c
@@ -2622,7 +2622,7 @@ create_recorder_instance_pipe(struct buffer_instance *instance,
int cpu, int *brass)
{
struct tracecmd_recorder *recorder;
- unsigned flags = recorder_flags | TRACECMD_RECORD_BLOCK;
+ unsigned flags = recorder_flags | TRACECMD_RECORD_BLOCK_SPLICE;
char *path;
if (instance->name)
@@ -4359,6 +4359,9 @@ enum {
OPT_funcstack = 254,
OPT_date = 255,
OPT_module = 256,
+ OPT_nofifos = 257,
+ OPT_cmdlines_size = 258,
+ OPT_poll = 259,
};
void trace_stop(int argc, char **argv)
@@ -4601,6 +4604,7 @@ static void parse_record_options(int argc,
{"quiet", no_argument, NULL, OPT_quiet},
{"help", no_argument, NULL, '?'},
{"module", required_argument, NULL, OPT_module},
+ {"poll", no_argument, NULL, OPT_poll},
{NULL, 0, NULL, 0}
};
@@ -4884,6 +4888,9 @@ static void parse_record_options(int argc,
ctx->instance->filter_mod = optarg;
ctx->filtered = 0;
break;
+ case OPT_poll:
+ recorder_flags |= TRACECMD_RECORD_POLL;
+ break;
case OPT_quiet:
case 'q':
quiet = 1;
diff --git a/trace-recorder.c b/trace-recorder.c
index 75290285..97dceccf 100644
--- a/trace-recorder.c
+++ b/trace-recorder.c
@@ -115,6 +115,18 @@ void tracecmd_free_recorder(struct tracecmd_recorder *recorder)
free(recorder);
}
+static void set_nonblock(struct tracecmd_recorder *recorder)
+{
+ long flags;
+
+ /* Do not block on reads for flushing */
+ flags = fcntl(recorder->trace_fd, F_GETFL);
+ fcntl(recorder->trace_fd, F_SETFL, flags | O_NONBLOCK);
+
+ /* Do not block on streams for write */
+ recorder->fd_flags |= 2; /* NON_BLOCK */
+}
+
struct tracecmd_recorder *
tracecmd_create_buffer_recorder_fd2(int fd, int fd2, int cpu, unsigned flags,
const char *buffer, int maxkb)
@@ -133,7 +145,7 @@ tracecmd_create_buffer_recorder_fd2(int fd, int fd2, int cpu, unsigned flags,
recorder->fd_flags = 1; /* SPLICE_F_MOVE */
- if (!(recorder->flags & TRACECMD_RECORD_BLOCK))
+ if (!(recorder->flags & TRACECMD_RECORD_BLOCK_SPLICE))
recorder->fd_flags |= 2; /* and NON_BLOCK */
/* Init to know what to free and release */
@@ -192,6 +204,9 @@ tracecmd_create_buffer_recorder_fd2(int fd, int fd2, int cpu, unsigned flags,
recorder->pipe_size = pipe_size;
}
+ if (recorder->flags & TRACECMD_RECORD_POLL)
+ set_nonblock(recorder);
+
free(path);
return recorder;
@@ -421,18 +436,6 @@ static long read_data(struct tracecmd_recorder *recorder)
return r;
}
-static void set_nonblock(struct tracecmd_recorder *recorder)
-{
- long flags;
-
- /* Do not block on reads for flushing */
- flags = fcntl(recorder->trace_fd, F_GETFL);
- fcntl(recorder->trace_fd, F_SETFL, flags | O_NONBLOCK);
-
- /* Do not block on streams for write */
- recorder->fd_flags |= 2; /* NON_BLOCK */
-}
-
long tracecmd_flush_recording(struct tracecmd_recorder *recorder)
{
char buf[recorder->page_size];
diff --git a/trace-usage.c b/trace-usage.c
index dc73d4d9..a9474ad3 100644
--- a/trace-usage.c
+++ b/trace-usage.c
@@ -57,6 +57,7 @@ static struct usage_help usage_help[] = {
" (use with caution)\n"
" --max-graph-depth limit function_graph depth\n"
" --no-filter include trace-cmd threads in the trace\n"
+ " --poll don't block while reading from the trace buffer\n"
},
{
"start",
--
2.31.1
Reference in New Issue View Git Blame Copy Permalink