Gator daemon, driver and related tools

The source code for gatord, gator.py and related tools.

License

• daemon, python, and notify are provided under GPL-2.0-only. See daemon/COPYING, python/COPYING, and notify/COPYING respectively.
• annotate is provided under the BSD-3-Clause license. See annotate/LICENSE.

This project contains code from other projects listed below. The original license text is included in those source files.

• libsensors source code in daemon/libsensors licensed under LGPL-2.1-or-later
• mxml source code in daemon/mxml licensed under APACHE-2.0 WITH Mini-XML-exception
• perf_event.h from Linux userspace kernel headers in daemon/k licensed under GPL-2.0-only WITH Linux-syscall-note

The pre-built gatord shipped with Streamline uses musl. For musl license information see the COPYRIGHT file shipped with Streamline, or https://git.musl-libc.org/cgit/musl/tree/COPYRIGHT

Contributing

Contributions are accepted under the same license as the associated subproject with developer sign-off as described in Contributing.

Purpose

Instructions on setting up Arm Streamline on the target.

A target agent (gator) is required to run on the Arm Linux target in order for Arm Streamline to operate. Gator requires Linux kernel version 3.4 or later.

Introduction

A Linux development environment with cross compiling tools is most likely required, depending on what is already created and provided.

Kernel configuration

Gator uses the Linux Perf API (perf_event_open) for most of its data collection. Additionally it will use ftrace tracepoints and some other common features such as debugfs/sysfs. Most users will not need to make any changes to their kernel configuration (and in many cases they cannot) as most recent Android devices and Linux distributions correctly configure their kernel with the required options. If you are a system integrator, or compiling your own kernel, the following options are required for correct functioning of Gator.

menuconfig options (depending on the kernel version, the location of these configuration settings within menuconfig may differ)

• General Setup
  • Timers subsystem
    • [*] High Resolution Timer Support (enables CONFIG_HIGH_RES_TIMERS)
  • Kernel Performance Events And Counters
    • [*] Kernel performance events and counters (enables CONFIG_PERF_EVENTS)
  • [*] Profiling Support (enables CONFIG_PROFILING)
• Kernel Features
  • [*] Use local timer interrupts (only required for SMP and for version before Linux 3.12, enables CONFIG_LOCAL_TIMERS)
  • [*] Enable hardware performance counter support for perf events (enables CONFIG_HW_PERF_EVENTS)
• CPU Power Management
  • CPU Frequency scaling
    • [*] CPU Frequency scaling (enables CONFIG_CPU_FREQ)
• Device Drivers
  • Graphics support
    • Arm GPU Configuration
      • Mali Midgard series support
        • [*] Streamline Debug support (enables CONFIG_MALI_GATOR_SUPPORT needed as part of Mali Midgard support)
• Kernel hacking
  • [*] Compile the kernel with debug info (optional, enables CONFIG_DEBUG_INFO)
  • [*] Tracers
    • [*] Trace process context switches and events (#)

(#) The "Trace process context switches and events" is not the only option that enables tracing (CONFIG_GENERIC_TRACER or CONFIG_TRACING as well as CONFIG_CONTEXT_SWITCH_TRACER) and may not be visible in menuconfig as an option if other trace configurations are enabled. Other trace configurations being enabled is sufficient to turn on tracing.

The configuration options:

• CONFIG_MODULES and MODULE_UNLOAD (not needed if the gator driver is built into the kernel)
• CONFIG_GENERIC_TRACER or CONFIG_TRACING
• CONFIG_CONTEXT_SWITCH_TRACER
• CONFIG_PROFILING
• CONFIG_HIGH_RES_TIMERS
• CONFIG_LOCAL_TIMERS (for SMP systems and kernel versions before 3.12)
• CONFIG_PERF_EVENTS and CONFIG_HW_PERF_EVENTS (kernel versions 3.0 and greater)
• CONFIG_DEBUG_INFO (optional, used for analyzing the kernel)
• CONFIG_CPU_FREQ (optional, provides frequency setting of the CPU)
• CONFIG_MALI_GATOR_SUPPORT (needed as part of Mali Midgard support)

These may be verified on a running system using /proc/config.gz (if this file exists) by running zcat /proc/config.gz | grep <option>. For example, confirming that CONFIG_PROFILING is enabled

> zcat /proc/config.gz | grep CONFIG_PROFILING
CONFIG_PROFILING=y

If a device tree is used it must include the pmu bindings, see Documentation/devicetree/bindings/arm/pmu.txt for details.

Use the pre-built gator daemon

The Streamline Setup Target tool will automatically install a pre-built gator daemon. This gator daemon should work in most cases so building the gator daemon is only required if the pre-built gator daemon doesn't work.

To improve portablility gatord is statically compiled against musl libc from http://www.musl-libc.org/download.html instead of glibc. The gator daemon will work correctly with either glibc or musl.

Building the gator daemon

Building gatord has the following requirements:

• C++11 supporting compiler
• Linux based build system

cp -r /path/to/streamline/gator/daemon .

For Linux targets,

cd daemon
make CROSS_COMPILE=<...>

gatord should now be created.

For Android targets (install the Android NDK appropriate for your target (ndk32 for 32-bit targets and ndk64 for 64-bit targets), see developer.android.com)

mv daemon jni
ndk-build

or execute /path/to/ndk/ndk-build if the ndk is not on your path.

gatord should now be created and located in libs/armeabi.

If you get an error like the following, upgrade to a more recent version of the android ndk

jni/PerfGroup.cpp: In function 'int sys_perf_event_open(perf_event_attr*, pid_t, int, int, long unsigned int)':
jni/PerfGroup.cpp:36:17: error: '__NR_perf_event_open' was not declared in this scope

To build gatord for aarch64 edit jni/Application.mk and replace armeabi-v7a with arm64-v8a. To build for ARM11 jni/Application.mk and replace armeabi-v7a with armeabi.

Running gator

As a root user

• Copy gatord into the target's filesystem.
• Ensure gatord has execute permissions: chmod +x gatord
• The daemon must be run with root privileges: sudo su gatord &

This configuration requires Linux 3.4 or later with a correctly configured kernel.

As a non-root user

• Copy gatord into the target's filesystem.
• Ensure gatord has execute permissions: chmod +x gatord
• Run the daemon: ./gatord &

This configuration provides a reduced set of software only CPU counters such as CPU utilization and process statistics, as well as Mali hardware counters on supported Mali platforms.

Perf PMU support

To check the perf PMUs support by your kernel, run ls /sys/bus/event_source/devices/ If you see something like ARMv7_Cortex_A## this indicates A## support. If you see CCI_400 this indicates CCI-400 support. If you see ccn, it indicates CCN support.

CCN

CCN requires a perf driver to work. The necessary perf driver has been merged into Linux 3.17 but can be backported to previous versions (see https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/diff/?id=a33b0daab73a0e08cc04459dd44b0121a8e8f81b and later bugfixes)

Compiling an application or shared library

Recommended compiler settings:

• -g: Debug information, such as line numbers, needed for best analysis results.
• -fno-inline: Speed improvement when processing the image files and most accurate analysis results.
• -fno-omit-frame-pointer: Arm EABI frame pointers allow recording of the call stack with each sample taken when in Arm state (i.e. not -mthumb).
• -marm: This option is required for ARMv7 and earlier if your compiler is configured with --with-mode=thumb, otherwise call stack unwinding will not work.

For Android ART, passing --no-strip-symbols to dex2oat will result in function names but not line numbers to be included in the dex files. This can be done by running setprop dalvik.vm.dex2oat-flags --no-strip-symbols on the device and then regenerating the dex files.

Polling /dev, /sys and /proc files

Gator supports reading arbitrary /dev, /sys and /proc files 10 times a second. It will either interpret the file contents as a number or use a POSIX extended regex to extract the number, see events-Filesystem.xml for examples.

Bugs

Kernels with CONFIG_CPU_PM enabled may produce invalid results on kernel versions prior to 4.6. The problem manifests as counters not showing any data, large spikes and non-sensible values for counters (e.g. Cycle Counter reading as very high). This issue stems from the fact that the kernel PMU driver does not save/restore state when the CPU is powered down/up. This issue is fixed in 4.6 so to resolve the issue either upgrade to a later kernel, or apply the fix to an older kernel. The patch for 4.6 that resolves the issue is found here https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=da4e4f18afe0f3729d68f3785c5802f786d36e34 - this patch has been tested as applying cleanly to 4.4 kernel and it may be possible to back port it to other versions as well. Users of this patch may also need to apply https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cbcc72e037b8a3eb1fad3c1ae22021df21c97a51 as well.

There is a bug in some Linux kernels where an Oops may occur when a core is offlined (user space gator only). The fix was merged into mainline in 3.14-rc5, see http://git.kernel.org/tip/e3703f8cdfcf39c25c4338c3ad8e68891cca3731, and has been backported to older kernels (3.4.83, 3.10.33, 3.12.14 and 3.13.6).

CPU PMU: CPUx reading wrong counter -1 in dmesg. To work around, update to the latest Linux kernel or use kernel space gator.

Scheduler switch resolutions are on exact millisecond boundaries. To work around, update to the latest Linux kernel or use kernel space gator.

There is a bug in some Linux kernels where perf misidentifies the CPU type. To see if you are affected by this, runls /sys/bus/event_source/devices/ and verify the listed processor type matches what is expected. For example, an A9 should show the following.

# ls /sys/bus/event_source/devices/
ARMv7_Cortex_A9  breakpoint  software  tracepoint

To work around the issue try upgrading to a later kernel.

On some versions of Android, annotations may not work unless SELinux is disabled by running # setenforce 0

Some targets do not correctly emit uevents when cores go on/offline. This will cause CPU Activity with user space gator to be either 0% or 100% on a given core and the Heat Map may show a large number of unresolved processes. To work around this issue, use kernel space gator. To test for this run # ./gatord -d | grep uevent When cores go on/offline with user space gator something similar to the following should be emitted

INFO: read(UEvent.cpp:61): uevent: [email protected]/devices/system/cpu/cpu1
INFO: read(UEvent.cpp:61): uevent: [email protected]/devices/system/cpu/cpu1

The cores that are on/offline can be checked by running # cat /sys/devices/system/cpu/cpu*/online This issue affects a given target if the on/offline cores shown by the cat command change but no cpu uevent is emitted.

On some older versions of Android, the following issue may occur when starting gatord when using ndk-build

# ./gatord
[1] + Stopped (signal)        ./gatord
#
[1]   Segmentation fault      ./gatord
#

Starting with Android-L only position independent executables (pie) are supported, but some older versions of Android do not support them. To avoid this issue, modify Android.mk and remove the references to pie.

Profiling the kernel (optional)

CONFIG_DEBUG_INFO must be enabled, see "Kernel configuration" section above.

Use vmlinux as the image for debug symbols in Streamline.

Drivers may be profiled using this method by statically linking the driver into the kernel image or adding the driver as an image to Streamline.