@@ -198,6 +198,21 @@ OPTIONS
inside the kernel. Using "-b 10000" on a machine with 4 CPUs will make
Ftrace have a total buffer size of 40 Megs.
+*--subbuf-size*::
+ The Linux kernel tracing ring buffer is broken up into sub-buffers.
+ These sub-buffers are typically the size of the architecture "page-size".
+ (4096 or x86). An event can only be as big as the data portion of a
+ sub-buffer, but in most cases that's not an issue. But the time the
+ writer takes to switch from one sub-buffer to the next has a bit more
+ overhead than adding events within the sub-buffer. By increasing its
+ size, it will allow bigger events (although that is seldom an issue)
+ but also speed up the tracing itself.
+
+ The downside of larger sub-buffers is that a "read" of the ring buffer
+ will pull the sub-buffer size out of the ring buffer and replace it
+ with a new sub-buffer. This may not have any real impact, but it may
+ change the behavior slightly. Or it may not!
+
*-B* 'buffer-name'::
If the kernel supports multiple buffers, this will add a buffer with
the given name. If the buffer name already exists, that buffer is just
@@ -286,6 +286,7 @@ struct buffer_instance {
int tracing_on_init_val;
int tracing_on_fd;
int buffer_size;
+ int subbuf_size;
int cpu_count;
int proxy_fd;
@@ -5099,10 +5099,7 @@ static char *get_date_to_ts(void)
static void set_buffer_size_instance(struct buffer_instance *instance)
{
int buffer_size = instance->buffer_size;
- char buf[BUFSIZ];
- char *path;
int ret;
- int fd;
if (is_guest(instance))
return;
@@ -5113,29 +5110,38 @@ static void set_buffer_size_instance(struct buffer_instance *instance)
if (buffer_size < 0)
die("buffer size must be positive");
- snprintf(buf, BUFSIZ, "%d", buffer_size);
+ ret = tracefs_instance_set_buffer_size(instance->tracefs, buffer_size, -1);
+ if (ret < 0)
+ warning("Can't set buffer size");
+}
- path = tracefs_instance_get_file(instance->tracefs, "buffer_size_kb");
- fd = open(path, O_WRONLY);
- if (fd < 0) {
- warning("can't open %s", path);
- goto out;
- }
+static void set_subbuf_size_instance(struct buffer_instance *instance)
+{
+ int subbuf_size = instance->subbuf_size;
+ int ret;
+
+ if (is_guest(instance))
+ return;
+
+ if (!subbuf_size)
+ return;
+
+ if (subbuf_size < 0)
+ die("sub-buffer size must be positive");
- ret = write(fd, buf, strlen(buf));
+ ret = tracefs_instance_set_subbuf_size(instance->tracefs, subbuf_size);
if (ret < 0)
- warning("Can't write to %s", path);
- close(fd);
- out:
- tracefs_put_tracing_file(path);
+ warning("Can't set sub-buffer size");
}
void set_buffer_size(void)
{
struct buffer_instance *instance;
- for_all_instances(instance)
+ for_all_instances(instance) {
set_buffer_size_instance(instance);
+ set_subbuf_size_instance(instance);
+ }
}
static int
@@ -5916,6 +5922,7 @@ enum {
OPT_temp = 262,
OPT_notimeout = 264,
OPT_daemonize = 265,
+ OPT_subbuf = 266,
};
void trace_stop(int argc, char **argv)
@@ -6343,6 +6350,7 @@ static void parse_record_options(int argc,
{"file-version", required_argument, NULL, OPT_file_ver},
{"proxy", required_argument, NULL, OPT_proxy},
{"temp", required_argument, NULL, OPT_temp},
+ {"subbuf-size", required_argument, NULL, OPT_subbuf},
{"daemonize", no_argument, NULL, OPT_daemonize},
{NULL, 0, NULL, 0}
};
@@ -6829,6 +6837,10 @@ static void parse_record_options(int argc,
die("TSC to nanosecond is not supported");
ctx->instance->flags |= BUFFER_FL_TSC2NSEC;
break;
+ case OPT_subbuf:
+ check_instance_die(ctx->instance, "--subbuf-size");
+ ctx->instance->subbuf_size = atoi(optarg);
+ break;
case OPT_poll:
cmd_check_die(ctx, CMD_set, *(argv+1), "--poll");
recorder_flags |= TRACECMD_RECORD_POLL;
@@ -55,6 +55,7 @@ static struct usage_help usage_help[] = {
" -G when profiling, set soft and hard irqs as global\n"
" --quiet print no output to the screen\n"
" --temp specify a directory to store the temp files used to create trace.dat\n"
+ " --subbuf-size to specify the sub-buffer size in kilobytes\n"
" --module filter module name\n"
" --by-comm used with --profile, merge events for related comms\n"
" --profile enable tracing options needed for report --profile\n"