[HN Gopher] Linux 6.3 Introducing Hardware Noise "Hwnoise" Tool
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       Linux 6.3 Introducing Hardware Noise "Hwnoise" Tool
        
       Author : isaacfrond
       Score  : 125 points
       Date   : 2023-02-21 12:07 UTC (10 hours ago)
        
 (HTM) web link (www.phoronix.com)
 (TXT) w3m dump (www.phoronix.com)
        
       | ilkkao wrote:
       | Needed to find this document to understand what noise means in
       | this context https://www.kernel.org/doc/html/next/trace/osnoise-
       | tracer.ht...
        
         | gorkish wrote:
         | Windows folks may be familiar with LatencyMon or DPC Checker
         | which do similar things on windows to find misbehaving hardware
         | or drivers which can cause issues for realtime/pseudo-realtime
         | applications like AV capture/mixing.
        
         | jmclnx wrote:
         | I read this but I do not get the point of OSNOISE. I was
         | thinking it would be used for better random number generation
         | but the doc does not seem to confirm that.
        
           | jabl wrote:
           | It's about jitter caused by the OS, or in this case HW (e.g.
           | due to SMM or similar shenanigans), that can be problematic
           | for real time or HPC applications.
        
           | monocasa wrote:
           | It's about measuring jitter caused by the OS. When you have a
           | large message passing system like you see in HPC
           | environments, delays in processing exactly the right messages
           | add up to huge failures of utilization because of the
           | dependency graph of work to be done. In the past I had even
           | seen national labs write their own Linux syscall compatible
           | kernels in order to combat jitter. For example:
           | https://github.com/HobbesOSR/kitten
        
             | guenthert wrote:
             | Afaik (Linux compatible) Lightweight kernels (LWK) have
             | been used in the past in lieu of Linux in (single
             | application) HPC scenarios in order to reduce context
             | switching and consequential cache misses and TLB thrashing.
             | 
             | I wouldn't know why 'the right message' needs to be
             | processed in a HPC application (as opposed to real time
             | applications). Where can I learn more about such?
        
         | taneq wrote:
         | Thanks! Even this still defines noise only in terms of
         | 'interference', and then takes a bit of digging to infer that
         | it's something to do with timing and interrupts, and so it's
         | probably jitter in execution time rather than referring to RF
         | interference or electrical noise. I'm no kernel hacker but I've
         | spent a lot of time close to the hardware and I've never heard
         | jitter referred to as 'noise'.
        
           | javier_e06 wrote:
           | I agree indeed. In statistical analysis or signal processing
           | noise is described as an element presenting data/energy other
           | than energy/data to be observed. I guess any data collecting
           | system can call noise anything that is filtered out from that
           | being measured.
        
       | _joel wrote:
       | As did most others in this thread it seems, assumed this was for
       | reducing RF noise, maybe reducing attack surface for some (tbf
       | difficult) exploits
        
         | sandworm101 wrote:
         | I'm worse. I thought it might be for actual physical
         | vibrations, such as can be measured by from HDD armatures or
         | dedicated detectors. If for nothing else, such things might
         | make for a good source of entropy.
        
           | heavyset_go wrote:
           | I thought it had to do with coil whine.
        
           | _joel wrote:
           | Obligatory https://www.youtube.com/watch?v=tDacjrSCeq4
        
             | wafflemaker wrote:
             | as a norwegian factory worker i'm appaled by lack of ear
             | protection.
        
       | kobekobe wrote:
       | jb\
        
       | alangibson wrote:
       | I'm definitely going to make use of this. I've currently got an
       | Odroid N2+ running realtime Linux with ~20 use latency under 100%
       | CPU load. I need something like this tool to get it even lower.
        
       | rurban wrote:
       | If they are talking about jitter they should call it jitter.
       | Noise is something completely different. The RT folks will just
       | shake their heads.
        
         | 2OEH8eoCRo0 wrote:
         | Jitter deals with signals. At this level we are not dealing
         | with signals but operating system tasks.
        
         | mlyle wrote:
         | Jitter and phase noise are closely related.
         | 
         | Here the units are a bit weird, but we're talking about
         | accumulated noise. Systems seek to reach 0.
         | 
         | This really means "no variability in performance", not just
         | "tasks start at the right time".
         | 
         | Performance noise is the correct term for what's measured. See
         | e.g.
         | https://www.researchgate.net/publication/353781546_Influence...
         | for a discussion.
        
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       (page generated 2023-02-21 23:02 UTC)