Erich Focht

VE program execution

Native vector engine (VE) programs are normally executed with the help of ve_exec, a program that interacts with the VE operating system daemon, allocates memory, creates a process inside VEOS, loads the VE binary into the VE memory and starts it there. While the native VE program is executed the ve_exec main thread is waiting for interrupts and exceptions raised by the program. Syscalls inside the VE program, for example, raise an exception through the monc instruction. Most of them are handled in the context of the ve_exec main thread on vector host (VH) side. Every VE porcess/thread has a corresponding thread on the VH which is handling its syscalls. This VH process is usually called pseudo process.

ve_exec does not need to be invoked explicitly. Normally it is registered in /proc/sys/fs/binfmt_misc/register as the ‘interpreter’ for VE ELF binaries.

Logging for the pseudo process

All components running in user space and linked to VEOS are using log4c as their logging facility. When you suspect that things are going wrong between ve_exec and VEOS, use this logging facility to check whether there are any suspicious error messages or warning from the pseudo process.

In order to enable the log4c logging facility copy the following sample log4crc file into the current working directory of the VE program.

Execute the VE program. log4c will create output files inside the working directory named ve_exec.log.<PID> with PID being the process ID of the executed program.

The default values in the sample log4crc file will reveal messages like:

[ve_exec_appender] 2018-07-05T16:28:23+0200 veos.pseudo_process.core INFO 410983 Setting default stack limit as unlimited
[ve_exec_appender] 2018-07-05T16:28:23+0200 veos.pseudo_process.core INFO 410983 default page size is : 0x4000000

Tweaking log4crc

The level of logging verbosity can be edited inside the log4crc file, for example by changing the priority attribute from “INFO” to “DEBUG” in the first line in the example below:

        <category name="veos.pseudo_process" priority="INFO" appender="ve_exec_appender" />
        <appender name="ve_exec_appender" layout="ve" type="stream" />

The appender attribute is pointing to the appender configuration line just below. You can change the layout attribute to “ve_debug” if you need more precise time stamps in the output. The type attribute is set to “stream”, which means that logs will simply be appended to the file, as long as the pseudo process is running.

Other appenders are configured with the type “rollingfile”. Their log files created in the current directory will be rotated similar to logrotate forr Linux system log files. When a file reaches a maximum size it will be renamed and a new log file will be opened. The number of log files kept is limited and configurable inside log4crc. Change it by editing the maxnum parameter in the rollingpolicy line inside the log4crc file:

        <rollingpolicy name="veos_command_rp" type="sizewin" maxsize="4194304" maxnum="10" />

Debug logs for VEOS

The VEOS VE operating system runs as a service in user space on the vector host. It also uses log4c as a logging facility and writes its logs into the directory /var/opt/nec/ve/veos.

The logging priority can be changed by the superuser by editing the log4crc file located in the directory /etc/opt/nec/ve/veos. After changing this file VEOS needs to be restarted by executing as root the command:

# systemctl restart ve-os-launcher@*.service

VEOS can be significantly slowed down by enabling too detailed logging. Don’t forget to reset the log4crc file to its old value after you captured the desired logs!