[LAU] reducing xruns (System configuration)

[david]

On 07/19/2018 11:56 PM, Ralf Mardorf wrote:
> On Fri, 20 Jul 2018 11:24:57 +0200, David Kastrup wrote:
>> So the idea to take this into low-latency realms with a view on
>> realtime effects seems a bit optimistic indeed.
> 
> ;)
> 
> On Thu, 19 Jul 2018 22:52:45 -1000, _another_ david wrote:
>> I first tried it with 4.13.x and decided that items like random
>> kernel panios, system freezes and crashes weren't very good ways to
>> defend against Spectre/Meltdown/DOS. ;)
> 
> Actually freezes and crashes do defend against attacks :D. But you are
> right, for Claws and Firefox I'm experiencing way to often serious
> issues and for virtualbox at least way to often an annoyance for an
> unexplained reason.
> 
> I at least should test using it with PTI disabled.
> 
> The current default on my machine is:
> 
> [rocketmouse at archlinux ~]$ ls -hAl /sys/devices/system/cpu/vulnerabilities/; cat /sys/devices/system/cpu/vulnerabilities/*
> total 0
> -r--r--r-- 1 root root 4.0K Jul 20 10:12 meltdown
> -r--r--r-- 1 root root 4.0K Jul 20 10:12 spec_store_bypass
> -r--r--r-- 1 root root 4.0K Jul 20 10:12 spectre_v1
> -r--r--r-- 1 root root 4.0K Jul 20 10:12 spectre_v2
> Mitigation: PTI
> Vulnerable
> Mitigation: __user pointer sanitization
> Mitigation: Full generic retpoline, IBPB, IBRS_FW
> 
> 'nopti' only would disable PTI, but keep the spectre mitigations. While
> PTI is part of the kernel, the spectre mitigations are likely part
> of the µcode. However, if I would run my CPU without the µcode, I
> perhaps would get rid of the spectre mitigation, but IIRC I
> unfortunately would get rid of TSC, too.

The Spectre mitigations don't seem to affect the performance on my 
desktop, which is running with PTI off but with the mitigation microcode 
patches. I also have Spectre mitigations on my Intel laptop with no 
performance impact.

-- 
David W. Jones
gnome at hawaii.rr.com
authenticity, honesty, community
http://dancingtreefrog.com