[LAU] performance problems after kernel/microcode update ?

[David Runge]

Hi Niklas,

On 2018-09-13 23:26:30 (+0200), Niklas Reppel wrote:
> Hi,
> 
> i recently updated my Arch linux system, to to the following version:
> 
> Linux 4.18.6-arch1-1-ARCH #1 SMP PREEMPT
> 
> Afterwards, i noticed that something has changed regarding the realtime
> permissions
> and that i had to install a new package called 'realtime-priviliges', which
> i never needed before,
> and subsequently add my main user to the 'realtime' group.
Please subscribe to the arch-proaudio mailing list. The change was
announced there [1].

> In that wake, i updated the processor microcode, which i didn't use at all
> before (there always was some
> error message during bootup, but nothing else).
> 
> After being able to start JACK in realtime again, i felt that there was a
> significant loss of performance.
> Things that didn't cause any dropouts before now start to crackle and
> gristle (as a sidenote, i mostly
> use SuperCollider to make sound).
> 
> Also, and this puzzled me especially, there were dropouts, but no XRuns ...
> normally, when i push the
> system to the limits, i get XRuns, that'd be expected. But now, it's
> dropouts without, and they start way
> earlier.
> 
> My machine has an Intel(R) Core(TM) i7-4600U CPU @ 2.10GHz Processor if that
> info is of user for anyone ...
> 
> Anybody else noticed something like that recently ?
It is very likely that the changes introduced to the Linux Kernel in
response to the spectre and meltdown security issues are causing this
in combination with (known to be) performance degrading Intel ucode.

However, I would not advice you to disable mitigations such as page
table isolation (PTI), unless you know about the implied risks!

Best,
David

[1] https://lists.archlinux.org/pipermail/arch-proaudio/2018-August/000191.html

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