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Linux kernel source tree
5e2ac8e857
On s390, and, in general, on all platforms where the respective event
supports auxiliary data gathering, the command:
# ./perf record -u 0 -aB --synth=no -- ./perf test -w thloop
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.011 MB perf.data ]
# ./perf report --stats | grep SAMPLE
#
does not generate samples in the perf.data file. On x86 the command:
# sudo perf record -e intel_pt// -u 0 ls
is broken too.
Looking at the sequence of calls in 'perf record' reveals this
behavior:
1. The event 'cycles' is created and enabled:
record__open()
+-> evlist__apply_filters()
+-> perf_bpf_filter__prepare()
+-> bpf_program.attach_perf_event()
+-> bpf_program.attach_perf_event_opts()
+-> __GI___ioctl(..., PERF_EVENT_IOC_ENABLE, ...)
The event 'cycles' is enabled and active now. However the event's
ring-buffer to store the samples generated by hardware is not
allocated yet.
2. The event's fd is mmap()ed to create the ring buffer:
record__open()
+-> record__mmap()
+-> record__mmap_evlist()
+-> evlist__mmap_ex()
+-> perf_evlist__mmap_ops()
+-> mmap_per_cpu()
+-> mmap_per_evsel()
+-> mmap__mmap()
+-> perf_mmap__mmap()
+-> mmap()
This allocates the ring buffer for the event 'cycles'. With mmap()
the kernel creates the ring buffer:
perf_mmap(): kernel function to create the event's ring
| buffer to save the sampled data.
|
+-> ring_buffer_attach(): Allocates memory for ring buffer.
| The PMU has auxiliary data setup function. The
| has_aux(event) condition is true and the PMU's
| stop() is called to stop sampling. It is not
| restarted:
|
| if (has_aux(event))
| perf_event_stop(event, 0);
|
+-> cpumsf_pmu_stop():
Hardware sampling is stopped. No samples are generated and saved
anymore.
3. After the event 'cycles' has been mapped, the event is enabled a
second time in:
__cmd_record()
+-> evlist__enable()
+-> __evlist__enable()
+-> evsel__enable_cpu()
+-> perf_evsel__enable_cpu()
+-> perf_evsel__run_ioctl()
+-> perf_evsel__ioctl()
+-> __GI___ioctl(., PERF_EVENT_IOC_ENABLE, .)
The second
ioctl(fd, PERF_EVENT_IOC_ENABLE, 0);
is just a NOP in this case. The first invocation in (1.) sets the
event::state to PERF_EVENT_STATE_ACTIVE. The kernel functions
perf_ioctl()
+-> _perf_ioctl()
+-> _perf_event_enable()
+-> __perf_event_enable()
return immediately because event::state is already set to
PERF_EVENT_STATE_ACTIVE.
This happens on s390, because the event 'cycles' offers the possibility
to save auxilary data. The PMU callbacks setup_aux() and free_aux() are
defined. Without both callback functions, cpumsf_pmu_stop() is not
invoked and sampling continues.
To remedy this, remove the first invocation of
ioctl(..., PERF_EVENT_IOC_ENABLE, ...).
in step (1.) Create the event in step (1.) and enable it in step (3.)
after the ring buffer has been mapped.
Output after:
# ./perf record -aB --synth=no -u 0 -- ./perf test -w thloop 2
[ perf record: Woken up 3 times to write data ]
[ perf record: Captured and wrote 0.876 MB perf.data ]
# ./perf report --stats | grep SAMPLE
SAMPLE events: 16200 (99.5%)
SAMPLE events: 16200
#
The software event succeeded both before and after the patch:
# ./perf record -e cpu-clock -aB --synth=no -u 0 -- \
./perf test -w thloop 2
[ perf record: Woken up 7 times to write data ]
[ perf record: Captured and wrote 2.870 MB perf.data ]
# ./perf report --stats | grep SAMPLE
SAMPLE events: 53506 (99.8%)
SAMPLE events: 53506
#
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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 reStructuredText 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.