Ninja overburdening system - how to tame it ?

Lone_Wolf · 2019-04-27 12:43:46

I maintain several AUR programs that use ninja as build system.

By default ninja uses nproc + 2 as jobs setting.
On my 12C/24T threadripper system with 16 Gib memory (ECC ram is expensive...) this results in my system becoming unresponsive and needing to swap parts out of memory .

I have $MAKEFLAGS=--j20 in makepkg.conf , but ninja doesn't use $MAKEFLAGS envvar .
I've found topics going back to 2015 about this and similar issues, https://github.com/ninja-build/ninja/issues/1482 looks promising.
No idea if/when it will be available from ninja.

executing ninja like this

ninja "$MAKEFLAGS" all ocaml_doc

does mean my system has capacity for other things and doesn't need to swap stuff out from memory.

This fails however if MAKEFLAGS is unset.

I can test whether MAKEFLAGS is set, and assign an arbitrary value like "-j$(nproc)" but feel this is still to high.
something like 85% of nproc , rounded down works well for me, but I have no idea how to calculate such a value and store it in MAKEFLAGS.

Before I implement such a solution in my aur packages using ninja i'd like to hear the opinion of other aur users & maintainers.

Last edited by Lone_Wolf (2019-04-27 12:59:12)

loqs · 2019-04-27 13:54:38

Looking at https://github.com/ninja-build/ninja/bl … il.cc#L493 ninja checks sched_getaffinity
so if you start makepkg with `taskset --cpu-list 0-11 makepkg` does that cause ninja to use 14 threads of your 24 core system?

Lone_Wolf · 2019-04-27 14:35:32

It does influence performance and load by a lot, but no idea how to check how many threads/ jobs ninja uses.

comparing performance of taskset 0-19 with that of -j20 suggests the performance is worse with taskset.
Maybe scheduler overhead is causing that ?

loqs · 2019-04-27 14:43:05

ninja adds 2 to the number of processes it uses when it detects more than 2 cores [1] so 0-19 should be equivalent to -j22 but run on 20 cores.

[1] https://github.com/ninja-build/ninja/bl … ja.cc#L228

Lone_Wolf · 2019-04-27 16:12:25

Reduced cpulist to 0-17 to have ninja run 20 jobs, this does bring performance with this specific task much closer to running with -j20.

Ninja is very fast and reliable, but I sometimes wish the effort to create ninja (and meson) had been spend to improve make / autotools.

Lone_Wolf · 2019-04-27 21:22:04

I build some more ninja packages and observed.
Using taskset is more restrictive then ninja -j option .

I'll use something like this :

if [[ ! $MAKEFLAGS ]]; then
  ninja
else
  ninja "$MAKEFLAGS"
fi

EDIT:
I've configured several packages this way now and it does appear to work fine.
I'm not marking this as solved yet, as both taskset and this if-then-else are workarounds.

Still hoping there are other options.

Last edited by Lone_Wolf (2019-04-28 11:13:38)

Lone_Wolf · 2019-04-29 11:50:02

Aur comments by lahwaacz made me realise ninja supports only a small part of the options MAKEFLAGS allow.
Running ninja "$MAKEFLAGS" does have a high chance of failing if those options are used.

I will switch to a dedicated envvar, NINJAFLAGS .

Add to makepkg.conf :

# limit ninja to 20 jobs
# requires special code in PKGBUILD
# see ninja --help for additonal options
NINJAFLAGS="-j20"

in PKGBUILD :

if [[ ! $NINJAFLAGS ]]; then
  ninja
else
  ninja "$NINJAFLAGS"
fi

This should allow users to configure ninja in whatever way they want without clashing with other programs.
Those that prefer ninja defaults have to do nothing.

Arch Linux

#1 2019-04-27 12:43:46

Ninja overburdening system - how to tame it ?

#2 2019-04-27 13:54:38

Re: Ninja overburdening system - how to tame it ?

#3 2019-04-27 14:35:32

Re: Ninja overburdening system - how to tame it ?

#4 2019-04-27 14:43:05

Re: Ninja overburdening system - how to tame it ?

#5 2019-04-27 16:12:25

Re: Ninja overburdening system - how to tame it ?

#6 2019-04-27 21:22:04

Re: Ninja overburdening system - how to tame it ?

#7 2019-04-29 11:50:02

Re: Ninja overburdening system - how to tame it ?

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