Vito Caputo
f82027042a
In scrutinizing the journal overhead of `systemctl status $service`
it became apparent that the matching engine was performing the unit
matches on every journal in my system, even ones containing nothing
relevant to the current boot.
This seemed strange and likely suboptimal to me, since there's likely
far more unit data to rifle through than boot IDs in any given
journal. The _BOOT_ID match seemed like it should be serving as an
early exit match on irrelevant journals, but that wasn't what seemed
to be happening.
As a quick experiment to see if I could get the _BOOT_ID match to be
something along the lines of a higher priority when matching, and try
early exit on these unrelated journals, I moved add_match_this_boot()
to after the unit match adds, inserting a conjunction between them.
The end result seems to be a very substantial performance gain in my
simple uncached tests, and I still get the expected journal output
from the `systemctl status $service` command:
----------------------------------------------------------------------
Unmodified systemctl times:
root@localhost:/# echo 2 > /proc/sys/vm/drop_caches
root@localhost:/# time systemctl --no-pager status dbus
● dbus.service - D-Bus System Message Bus
Loaded: loaded (/lib/systemd/system/dbus.service; static; vendor preset: enabled)
Active: active (running) since Sun 2020-10-25 17:03:05 PDT; 1 day 6h ago
Docs: man:dbus-daemon(1)
Main PID: 572 (dbus-daemon)
Memory: 2.8M
CPU: 110ms
CGroup: /system.slice/dbus.service
└─572 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation
Oct 25 17:03:05 localhost systemd[1]: Started D-Bus System Message Bus.
Oct 25 17:06:26 localhost dbus[572]: [system] Activating via systemd: service name='org.freedesktop.machine1' unit='dbus-org.freedesktop.machine1.service'
Oct 25 17:06:26 localhost dbus[572]: [system] Successfully activated service 'org.freedesktop.machine1'
real 0m0.695s
user 0m0.005s
sys 0m0.043s
root@localhost:/# echo 2 > /proc/sys/vm/drop_caches
root@localhost:/# time systemctl --no-pager status dbus
● dbus.service - D-Bus System Message Bus
Loaded: loaded (/lib/systemd/system/dbus.service; static; vendor preset: enabled)
Active: active (running) since Sun 2020-10-25 17:03:05 PDT; 1 day 6h ago
Docs: man:dbus-daemon(1)
Main PID: 572 (dbus-daemon)
Memory: 2.8M
CPU: 110ms
CGroup: /system.slice/dbus.service
└─572 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation
Oct 25 17:03:05 localhost systemd[1]: Started D-Bus System Message Bus.
Oct 25 17:06:26 localhost dbus[572]: [system] Activating via systemd: service name='org.freedesktop.machine1' unit='dbus-org.freedesktop.machine1.service'
Oct 25 17:06:26 localhost dbus[572]: [system] Successfully activated service 'org.freedesktop.machine1'
real 0m0.696s
user 0m0.003s
sys 0m0.046s
root@localhost:/# echo 2 > /proc/sys/vm/drop_caches
root@localhost:/# time systemctl --no-pager status dbus
● dbus.service - D-Bus System Message Bus
Loaded: loaded (/lib/systemd/system/dbus.service; static; vendor preset: enabled)
Active: active (running) since Sun 2020-10-25 17:03:05 PDT; 1 day 6h ago
Docs: man:dbus-daemon(1)
Main PID: 572 (dbus-daemon)
Memory: 2.8M
CPU: 110ms
CGroup: /system.slice/dbus.service
└─572 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation
Oct 25 17:03:05 localhost systemd[1]: Started D-Bus System Message Bus.
Oct 25 17:06:26 localhost dbus[572]: [system] Activating via systemd: service name='org.freedesktop.machine1' unit='dbus-org.freedesktop.machine1.service'
Oct 25 17:06:26 localhost dbus[572]: [system] Successfully activated service 'org.freedesktop.machine1'
real 0m0.694s
user 0m0.006s
sys 0m0.041s
----------------------------------------------------------------------
Modified systemctl including this commit:
root@localhost:/home/vc/gh/systemd/build# echo 2 > /proc/sys/vm/drop_caches
root@localhost:/home/vc/gh/systemd/build# time ./systemctl --no-pager status dbus
● dbus.service - D-Bus System Message Bus
Loaded: loaded (/lib/systemd/system/dbus.service; static)
Active: active (running) since Sun 2020-10-25 17:03:05 PDT; 1 day 6h ago
TriggeredBy: ● dbus.socket
Docs: man:dbus-daemon(1)
Main PID: 572 (dbus-daemon)
Memory: 2.8M
CPU: 110ms
CGroup: /system.slice/dbus.service
└─572 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation
Oct 25 17:03:05 localhost systemd[1]: Started D-Bus System Message Bus.
Oct 25 17:06:26 localhost dbus[572]: [system] Activating via systemd: service name='org.freedesktop.machine1' unit='dbus-org.freedesktop.machine1.service'
Oct 25 17:06:26 localhost dbus[572]: [system] Successfully activated service 'org.freedesktop.machine1'
real 0m0.168s
user 0m0.003s
sys 0m0.016s
root@localhost:/home/vc/gh/systemd/build# echo 2 > /proc/sys/vm/drop_caches
root@localhost:/home/vc/gh/systemd/build# time ./systemctl --no-pager status dbus
● dbus.service - D-Bus System Message Bus
Loaded: loaded (/lib/systemd/system/dbus.service; static)
Active: active (running) since Sun 2020-10-25 17:03:05 PDT; 1 day 6h ago
TriggeredBy: ● dbus.socket
Docs: man:dbus-daemon(1)
Main PID: 572 (dbus-daemon)
Memory: 2.8M
CPU: 110ms
CGroup: /system.slice/dbus.service
└─572 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation
Oct 25 17:03:05 localhost systemd[1]: Started D-Bus System Message Bus.
Oct 25 17:06:26 localhost dbus[572]: [system] Activating via systemd: service name='org.freedesktop.machine1' unit='dbus-org.freedesktop.machine1.service'
Oct 25 17:06:26 localhost dbus[572]: [system] Successfully activated service 'org.freedesktop.machine1'
real 0m0.167s
user 0m0.005s
sys 0m0.013s
root@localhost:/home/vc/gh/systemd/build# echo 2 > /proc/sys/vm/drop_caches
root@localhost:/home/vc/gh/systemd/build# time ./systemctl --no-pager status dbus
● dbus.service - D-Bus System Message Bus
Loaded: loaded (/lib/systemd/system/dbus.service; static)
Active: active (running) since Sun 2020-10-25 17:03:05 PDT; 1 day 6h ago
TriggeredBy: ● dbus.socket
Docs: man:dbus-daemon(1)
Main PID: 572 (dbus-daemon)
Memory: 2.8M
CPU: 110ms
CGroup: /system.slice/dbus.service
└─572 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation
Oct 25 17:03:05 localhost systemd[1]: Started D-Bus System Message Bus.
Oct 25 17:06:26 localhost dbus[572]: [system] Activating via systemd: service name='org.freedesktop.machine1' unit='dbus-org.freedesktop.machine1.service'
Oct 25 17:06:26 localhost dbus[572]: [system] Successfully activated service 'org.freedesktop.machine1'
real 0m0.170s
user 0m0.005s
sys 0m0.014s
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