Enable Pressure Stall Information (PSI) on Void Linux

There are two configurations for Pressure Stall Information (PSI) feature in kernel: CONFIG_PSI for supporting PSI or not and CONFIG_PSI_DEFAULT_DISABLED for diabling PSI or not. Check my Void Linux configurations:

$ zgrep PSI /proc/config.gz
CONFIG_PSI=y
CONFIG_PSI_DEFAULT_DISABLED=y

We can see PSI is disabled by default, and it will incur following errors:

$ cat /proc/pressure/cpu
cat: /proc/pressure/cpu: Operation not supported

To enable this feature, add “psi=1” for GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub file:

$ cat /etc/default/grub
#
# Configuration file for GRUB.
#
......
GRUB_CMDLINE_LINUX_DEFAULT="loglevel=4 slub_debug=P page_poison=1 psi=1"

Then regenerating the grub configuration and reboot:

$ sudo grub-mkconfig -o /boot/grub/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-5.2.13_1
Found initrd image: /boot/initramfs-5.2.13_1.img
done
$sudo reboot

The PSI is enabled:

$ cat /proc/pressure/cpu
some avg10=0.00 avg60=0.00 avg300=0.00 total=890919

References:
Getting Started with PSI;
Where are the current kernel build options stored?;
grub.

Beware of using “perf top” and “perf record” simultaneously

My OS is RHEL7 and my perf version is:

perf version 3.10.0-514.16.1.el7.x86_64.debug

My application bonds some threads with dedicated CPUs (1-13,15-27,31-41,43-55). During its running, I use “perf top” to observe these dedicated CPUs:

$ sudo perf top -C 1-13,15-27,31-41,43-55

At the same time, if I use “perf record” to sample the whole process:

$ sudo perf record -g -p 22530

“perf record” can’t sample threads running on CPUs monitored by “perf top“. So please be cautious when using “perf top” and “perf record” simultaneously.

Build open source projects without configure script

Some open source projects don’t provide configure script. Take nio-tlsf as an example. You can see there are only Makefile.am and configure.ac. For projects like it, you need to run autoreconf to generate configure script:

$ autoreconf
aclocal: warning: couldn't open directory 'm4': No such file or directory
configure.ac:21: error: required file 'build-aux/compile' not found
configure.ac:21:   'automake --add-missing' can install 'compile'
configure.ac:22: error: required file 'build-aux/config.guess' not found
configure.ac:22:   'automake --add-missing' can install 'config.guess'
configure.ac:22: error: required file 'build-aux/config.sub' not found
configure.ac:22:   'automake --add-missing' can install 'config.sub'
configure.ac:15: error: required file 'build-aux/install-sh' not found
configure.ac:15:   'automake --add-missing' can install 'install-sh'
configure.ac:22: error: required file 'build-aux/ltmain.sh' not found
configure.ac:15: error: required file 'build-aux/missing' not found
configure.ac:15:   'automake --add-missing' can install 'missing'
Makefile.am: error: required file 'build-aux/depcomp' not found
Makefile.am:   'automake --add-missing' can install 'depcomp'
autoreconf: automake failed with exit status: 1

There are so many “... not found” errors, and “autoreconf --install” can fix them:

$ autoreconf --install
aclocal: warning: couldn't open directory 'm4': No such file or directory
libtoolize: putting auxiliary files in AC_CONFIG_AUX_DIR, 'build-aux'.
libtoolize: copying file 'build-aux/ltmain.sh'
libtoolize: putting macros in AC_CONFIG_MACRO_DIRS, 'm4'.
libtoolize: copying file 'm4/libtool.m4'
libtoolize: copying file 'm4/ltoptions.m4'
libtoolize: copying file 'm4/ltsugar.m4'
libtoolize: copying file 'm4/ltversion.m4'
libtoolize: copying file 'm4/lt~obsolete.m4'
configure.ac:21: installing 'build-aux/compile'
configure.ac:22: installing 'build-aux/config.guess'
configure.ac:22: installing 'build-aux/config.sub'
configure.ac:15: installing 'build-aux/install-sh'
configure.ac:15: installing 'build-aux/missing'
Makefile.am: installing 'build-aux/depcomp'

Now configure script is generated successfully, and you can build the whole project.

Use alignof in gcc

alignof is defined in stdalign.h for gcc:

$ cat /usr/lib/gcc/x86_64-unknown-linux-gnu/9.1.0/include/stdalign.h
......
#ifndef _STDALIGN_H
#define _STDALIGN_H

#ifndef __cplusplus

#define alignas _Alignas
#define alignof _Alignof

#define __alignas_is_defined 1
#define __alignof_is_defined 1

#endif

#endif  /* stdalign.h */

To use alignof, stdalign.h must be included, otherwise following errors will be reported:

......
warning: implicit declaration of function 'alignof' [-Wimplicit-function-declaration]
    3 |  return alignof(int);
      |         ^~~~~~~
 error: expected expression before

It is no need to include any header files to use _Alignof and __alignof__.