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Tuning the system by disabling mitigations
Posted: Wed Feb 13, 2019 2:43 pm
by bluebell
There are some mitigations against meltdown and spectre, most important for cloud and server providers.
If you run a single user machine you may consider switching off those mitigations because they eat CPU power.
On my Core i5 that got problems with some big Qtractor projects I'll try in the next days:
Code: Select all
pti=off spectre_v2=off l1tf=off nospec_store_bypass_disable no_stf_barrier
in the GRUB boot cmdline.
Re: Tuning the system by disabling mitigations
Posted: Wed Feb 13, 2019 6:04 pm
by bluebell
No noticeble effect. OK, was worth a try.
Re: Tuning the system by disabling mitigations
Posted: Wed Feb 13, 2019 8:33 pm
by sysrqer
Did you run any kind of benchmark test? It would be interesting to know what the difference is although if it's not noticeable maybe it is not relevant.
Re: Tuning the system by disabling mitigations
Posted: Thu Feb 14, 2019 12:30 pm
by bluebell
sysrqer wrote:Did you run any kind of benchmark test? It would be interesting to know what the difference is although if it's not noticeable maybe it is not relevant.
Only "can I make jackd's buffer size smaller for a given Qtractor project". In my case: no. So I couldn't see any difference.
Re: Tuning the system by disabling mitigations
Posted: Thu Feb 14, 2019 12:55 pm
by Musicteacher
This is a very rough scale (buffer size). Buffer size usually is changed in powers of 2, one cannot seriously think that system speed goes up by a factor of 2!
What about: How many plugins of a given type can I use befor I get xruns? Like "50 instances of my favorite synth" vs "52 instances ..."
Re: Tuning the system by disabling mitigations
Posted: Thu Feb 14, 2019 1:32 pm
by merlyn
A good practical test is how many notes on pianoteq, since the DSP load goes up with the number of notes played.
Re: Tuning the system by disabling mitigations
Posted: Sat Mar 16, 2019 6:54 pm
by bluebell
I tested with xruncounter and got some interesting results.
Hardware: Notebook with Intel(R) Core(TM) i7-7700T CPU @ 2.90GHz
Kernel: Linux bubu 4.16.12-rt5-avl1 #12 SMP PREEMPT RT Thu Jun 14 04:35:48 EDT 2018 x86_64 x86_64 x86_64 GNU/Linux
jack2 with -n2 -p 128
With mitigations I got the 1st xrun at 69%, 62%, 67% (3 runs).
Without mitigations I got the 1st xrun at 74%, 70%, 71%
So disabling the mitigations seems to enable a slight performance boost.