commit	79249b0897016cdcd1344f4c5e8876fbf433de3e	[log] [tgz]
author	Mark Salyzyn <salyzyn@google.com>	Tue Nov 07 08:19:20 2017 -0800
committer	Mark Salyzyn <salyzyn@google.com>	Thu Dec 07 09:41:48 2017 -0800
tree	6b7a479b3a82507a0070777d1be3e6fa73b78cc3
parent	6f9c35ded294ca7b0b8f9042f705cbfca1ec8518 [diff]

bionic: add vdso clock_getres

clock_getres() should not be a hot call, nevertheless it is
~6-7 times faster for supported clock ids if it uses
__vdso_clock_getres if available.  There is a 3% performance
penalty for unsupported clock ids via __vdso_clock_getres with
respect to a direct syscall.

[TL;DR]

w/vdso32 kernel patches, locked cores to MAX, little cores only.

BEFORE:

hikey960 vdso (aarch64):

----------------------------------------------------------------------
Benchmark                               Time           CPU Iterations
----------------------------------------------------------------------
BM_time_clock_getres                  126 ns        126 ns    5577874
BM_time_clock_getres_syscall          127 ns        127 ns    5505016
BM_time_clock_getres_REALTIME         126 ns        126 ns    5574682
BM_time_clock_getres_BOOTTIME         126 ns        126 ns    5575237
BM_time_clock_getres_TAI              126 ns        126 ns    5576810
BM_time_clock_getres_unsupported      128 ns        128 ns    5480189

hikey960 vdso32 (aarch32):

----------------------------------------------------------------------
Benchmark                               Time           CPU Iterations
----------------------------------------------------------------------
BM_time_clock_getres                  199 ns        199 ns    3508708
BM_time_clock_getres_syscall          220 ns        220 ns    3184676
BM_time_clock_getres_REALTIME         199 ns        199 ns    3509697
BM_time_clock_getres_BOOTTIME         199 ns        199 ns    3513551
BM_time_clock_getres_TAI              200 ns        199 ns    3512412
BM_time_clock_getres_unsupported      196 ns        196 ns    3575609

x86_64 (glibc):

---------------------------------------------------------------------
Benchmark                              Time           CPU Iterations
---------------------------------------------------------------------
BM_time_clock_getres                 252 ns        252 ns    2370263
BM_time_clock_getres_syscall         215 ns        215 ns    3287497
BM_time_clock_getres_REALTIME        214 ns        214 ns    3294228
BM_time_clock_getres_BOOTTIME        213 ns        213 ns    3277519
BM_time_clock_getres_TAI             213 ns        213 ns    3294991
BM_time_clock_getres_unsupported     206 ns        206 ns    3450654

imx7d_pico IOT nyc (w/arm,cpu-registers-not-fw-configured) (armv7a):
(Virtual Timers)

Benchmark                           Time(ns)    CPU(ns) Iterations
------------------------------------------------------------------
BM_time_clock_getres                      16        345    2000000
BM_time_clock_getres_syscall              16        339    2121212
BM_time_clock_getres_REALTIME             17        350    2058824
BM_time_clock_getres_BOOTTIME             17        345    2000000
BM_time_clock_getres_TAI                  16        350    2000000
BM_time_clock_getres_unsupported          13        284    2500000

AFTER:

hikey960 vdso (aarch64):

---------------------------------------------------------------------
Benchmark                              Time           CPU Iterations
---------------------------------------------------------------------
BM_time_clock_getres                  18 ns         18 ns   37880389
BM_time_clock_getres_syscall         127 ns        127 ns    5520029
BM_time_clock_getres_REALTIME         18 ns         18 ns   37879962
BM_time_clock_getres_BOOTTIME         19 ns         18 ns   37878361
BM_time_clock_getres_TAI             131 ns        131 ns    5368484
BM_time_clock_getres_unsupported      97 ns         97 ns    7182864

hikey960 vdso32 (aarch32):

---------------------------------------------------------------------
Benchmark                              Time           CPU Iterations
---------------------------------------------------------------------
BM_time_clock_getres                  36 ns         36 ns   19205240
BM_time_clock_getres_syscall         212 ns        212 ns    3297100
BM_time_clock_getres_REALTIME         36 ns         36 ns   19219109
BM_time_clock_getres_BOOTTIME         36 ns         36 ns   19222490
BM_time_clock_getres_TAI             206 ns        206 ns    3402868
BM_time_clock_getres_unsupported     159 ns        159 ns    4409492

imx7d_pico IOT nyc (wo/arm,cpu-registers-not-fw-configured) (armv7a):
(Physical Timers)

Benchmark                           Time(ns)    CPU(ns) Iterations
------------------------------------------------------------------
BM_time_clock_getres                       2         48   14000000
BM_time_clock_getres_syscall              14        335    2058824
BM_time_clock_getres_REALTIME              2         49   14583333
BM_time_clock_getres_BOOTTIME              2         48   14000000
BM_time_clock_getres_TAI                  14        350    2058824
BM_time_clock_getres_unsupported           8        203    3500000

Test: taskset F \
        /data/benchmarktest{64}/bionic-benchmarks/bionic-benchmarks \
        --bionic_xml=vdso.xml --benchmark_filter=BM_time_clock_getres*
Bug: 63737556
Change-Id: I80c0a5106625d76720287f715fcf145d2aad1705

libc/arch-arm/syscalls/__clock_getres.S[Renamed from libc/arch-arm/syscalls/clock_getres.S - diff]
libc/arch-arm64/syscalls/__clock_getres.S[Renamed from libc/arch-arm64/syscalls/clock_getres.S - diff]
libc/arch-mips/syscalls/__clock_getres.S[Renamed from libc/arch-mips/syscalls/clock_getres.S - diff]
libc/arch-mips64/syscalls/__clock_getres.S[Renamed from libc/arch-mips64/syscalls/clock_getres.S - diff]
libc/arch-x86/syscalls/__clock_getres.S[Renamed from libc/arch-x86/syscalls/clock_getres.S - diff]
libc/arch-x86_64/syscalls/__clock_getres.S[Renamed from libc/arch-x86_64/syscalls/clock_getres.S - diff]
libc/bionic/vdso.cpp[diff]
libc/private/bionic_vdso.h[diff]

8 files changed

tree: 6b7a479b3a82507a0070777d1be3e6fa73b78cc3

README.md

Using bionic

See the additional documentation.

Working on bionic

What are the big pieces of bionic?

libc/ --- libc.so, libc.a

The C library. Stuff like fopen(3) and kill(2).

libm/ --- libm.so, libm.a

The math library. Traditionally Unix systems kept stuff like sin(3) and cos(3) in a separate library to save space in the days before shared libraries.

libdl/ --- libdl.so

The dynamic linker interface library. This is actually just a bunch of stubs that the dynamic linker replaces with pointers to its own implementation at runtime. This is where stuff like dlopen(3) lives.

libstdc++/ --- libstdc++.so

The C++ ABI support functions. The C++ compiler doesn't know how to implement thread-safe static initialization and the like, so it just calls functions that are supplied by the system. Stuff like __cxa_guard_acquire and __cxa_pure_virtual live here.

linker/ --- /system/bin/linker and /system/bin/linker64

The dynamic linker. When you run a dynamically-linked executable, its ELF file has a DT_INTERP entry that says "use the following program to start me". On Android, that's either linker or linker64 (depending on whether it's a 32-bit or 64-bit executable). It's responsible for loading the ELF executable into memory and resolving references to symbols (so that when your code tries to jump to fopen(3), say, it lands in the right place).

tests/ --- unit tests

The tests/ directory contains unit tests. Roughly arranged as one file per publicly-exported header file.

benchmarks/ --- benchmarks

The benchmarks/ directory contains benchmarks, with its own documentation.

What's in libc/?

Adding system calls

Adding a system call usually involves:

Add entries to SYSCALLS.TXT. See SYSCALLS.TXT itself for documentation on the format.
Run the gensyscalls.py script.
Add constants (and perhaps types) to the appropriate header file. Note that you should check to see whether the constants are already in kernel uapi header files, in which case you just need to make sure that the appropriate POSIX header file in libc/include/ includes the relevant file or files.
Add function declarations to the appropriate header file.
Add the function name to the correct section in libc/libc.map.txt and run ./libc/tools/genversion-scripts.py.
Add at least basic tests. Even a test that deliberately supplies an invalid argument helps check that we're generating the right symbol and have the right declaration in the header file, and that you correctly updated the maps in step 5. (You can use strace(1) to confirm that the correct system call is being made.)

Updating kernel header files

As mentioned above, this is currently a two-step process:

Use generate_uapi_headers.sh to go from a Linux source tree to appropriate contents for external/kernel-headers/.
Run update_all.py to scrub those headers and import them into bionic.

Note that if you're actually just trying to expose device-specific headers to build your device drivers, you shouldn't modify bionic. Instead use TARGET_DEVICE_KERNEL_HEADERS and friends described in config.mk.

Updating tzdata

This is fully automated (and these days handled by the libcore team, because they own icu, and that needs to be updated in sync with bionic):

Run update-tzdata.py in external/icu/tools/.

Verifying changes

If you make a change that is likely to have a wide effect on the tree (such as a libc header change), you should run make checkbuild. A regular make will not build the entire tree; just the minimum number of projects that are required for the device. Tests, additional developer tools, and various other modules will not be built. Note that make checkbuild will not be complete either, as make tests covers a few additional modules, but generally speaking make checkbuild is enough.

Running the tests

The tests are all built from the tests/ directory.

Device tests

$ mma # In $ANDROID_ROOT/bionic.
$ adb root && adb remount && adb sync
$ adb shell /data/nativetest/bionic-unit-tests/bionic-unit-tests
$ adb shell \
    /data/nativetest/bionic-unit-tests-static/bionic-unit-tests-static
# Only for 64-bit targets
$ adb shell /data/nativetest64/bionic-unit-tests/bionic-unit-tests
$ adb shell \
    /data/nativetest64/bionic-unit-tests-static/bionic-unit-tests-static

Note that we use our own custom gtest runner that offers a superset of the options documented at https://github.com/google/googletest/blob/master/googletest/docs/AdvancedGuide.md#running-test-programs-advanced-options, in particular for test isolation and parallelism (both on by default).

Device tests via CTS

Most of the unit tests are executed by CTS. By default, CTS runs as a non-root user, so the unit tests must also pass when not run as root. Some tests cannot do any useful work unless run as root. In this case, the test should check getuid() == 0 and do nothing otherwise (typically we log in this case to prevent accidents!). Obviously, if the test can be rewritten to not require root, that's an even better solution.

Currently, the list of bionic CTS tests is generated at build time by running a host version of the test executable and dumping the list of all tests. In order for this to continue to work, all architectures must have the same number of tests, and the host version of the executable must also have the same number of tests.

Running the gtests directly is orders of magnitude faster than using CTS, but in cases where you really have to run CTS:

$ make cts # In $ANDROID_ROOT.
$ adb unroot # Because real CTS doesn't run as root.
# This will sync any *test* changes, but not *code* changes:
$ cts-tradefed \
    run singleCommand cts --skip-preconditions -m CtsBionicTestCases

Host tests

The host tests require that you have lunched either an x86 or x86_64 target. Note that due to ABI limitations (specifically, the size of pthread_mutex_t), 32-bit bionic requires PIDs less than 65536. To enforce this, set /proc/sys/kernel/pid_max to 65536.

$ ./tests/run-on-host.sh 32
$ ./tests/run-on-host.sh 64   # For x86_64-bit *targets* only.

You can supply gtest flags as extra arguments to this script.

Against glibc

As a way to check that our tests do in fact test the correct behavior (and not just the behavior we think is correct), it is possible to run the tests against the host's glibc.

$ ./tests/run-on-host.sh glibc

Gathering test coverage

For either host or target coverage, you must first:

$ export NATIVE_COVERAGE=true
- Note that the build system is ignorant to this flag being toggled, i.e. if you change this flag, you will have to manually rebuild bionic.
Set bionic_coverage=true in libc/Android.mk and libm/Android.mk.

Coverage from device tests

$ mma
$ adb sync
$ adb shell \
    GCOV_PREFIX=/data/local/tmp/gcov \
    GCOV_PREFIX_STRIP=`echo $ANDROID_BUILD_TOP | grep -o / | wc -l` \
    /data/nativetest/bionic-unit-tests/bionic-unit-tests
$ acov

acov will pull all coverage information from the device, push it to the right directories, run lcov, and open the coverage report in your browser.

Coverage from host tests

First, build and run the host tests as usual (see above).

$ croot
$ lcov -c -d $ANDROID_PRODUCT_OUT -o coverage.info
$ genhtml -o covreport coverage.info # or lcov --list coverage.info

The coverage report is now available at covreport/index.html.

Attaching GDB to the tests

Bionic's test runner will run each test in its own process by default to prevent tests failures from impacting other tests. This also has the added benefit of running them in parallel, so they are much faster.

However, this also makes it difficult to run the tests under GDB. To prevent each test from being forked, run the tests with the flag --no-isolate.

32-bit ABI bugs

See 32-bit ABI bugs.