6657a099e1
AUX area traces can produce too much data to record successfully or
analyze subsequently. Add another means to reduce data collection by
allowing multiple recording time ranges.
This is useful, for instance, in cases where a workload produces
predictably reproducible events in specific time ranges.
Today we only have perf record -D <msecs> to start at a specific region, or
some complicated approach using snapshot mode and external scripts sending
signals or using the fifos. But these approaches are difficult to set up
compared with simply having perf do it.
Extend perf record option -D/--delay option to specifying relative time
stamps for start stop controlled by perf with the right time offset, for
instance:
perf record -e intel_pt// -D 10-20,30-40
to record 10ms to 20ms into the trace and 30ms to 40ms.
Example:
The example workload is:
$ cat repeat-usleep.c
int usleep(useconds_t usec);
int usage(int ret, const char *msg)
{
if (msg)
fprintf(stderr, "%s\n", msg);
fprintf(stderr, "Usage is: repeat-usleep <microseconds>\n");
return ret;
}
int main(int argc, char *argv[])
{
unsigned long usecs;
char *end_ptr;
if (argc != 2)
return usage(1, "Error: Wrong number of arguments!");
errno = 0;
usecs = strtoul(argv[1], &end_ptr, 0);
if (errno || *end_ptr || usecs > UINT_MAX)
return usage(1, "Error: Invalid argument!");
while (1) {
int ret = usleep(usecs);
if (ret & errno != EINTR)
return usage(1, "Error: usleep() failed!");
}
return 0;
}
$ perf record -e intel_pt//u --delay 10-20,40-70,110-160 -- ./repeat-usleep 500
Events disabled
Events enabled
Events disabled
Events enabled
Events disabled
Events enabled
Events disabled
[ perf record: Woken up 5 times to write data ]
[ perf record: Captured and wrote 0.204 MB perf.data ]
Terminated
A dlfilter is used to determine continuous data collection (timestamps
less than 1ms apart):
$ cat dlfilter-show-delays.c
static __u64 start_time;
static __u64 last_time;
int start(void **data, void *ctx)
{
printf("%-17s\t%-9s\t%-6s\n", " Time", " Duration", " Delay");
return 0;
}
int filter_event_early(void *data, const struct perf_dlfilter_sample *sample, void *ctx)
{
__u64 delta;
if (!sample->time)
return 1;
if (!last_time)
goto out;
delta = sample->time - last_time;
if (delta < 1000000)
goto out2;;
printf("%17.9f\t%9.1f\t%6.1f\n", start_time / 1000000000.0, (last_time - start_time) / 1000000.0, delta / 1000000.0);
out:
start_time = sample->time;
out2:
last_time = sample->time;
return 1;
}
int stop(void *data, void *ctx)
{
printf("%17.9f\t%9.1f\n", start_time / 1000000000.0, (last_time - start_time) / 1000000.0);
return 0;
}
The result shows the times roughly match the --delay option:
$ perf script --itrace=qb --dlfilter dlfilter-show-delays.so
Time Duration Delay
39215.302317300 9.7 20.5
39215.332480217 30.4 40.9
39215.403837717 49.8
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexey Bayduraev <alexey.v.bayduraev@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20220824072814.16422-6-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.