[External] dbus-sensors issue

[Jeff9 Chan(陳松儉_ASRockRack)]

Thanks a lot!

best regards

Jeff Chan

-----Original Message-----
From: patrick at stwcx.xyz <patrick at stwcx.xyz> 
Sent: Saturday, February 8, 2025 1:04 AM
To: Jian Zhang <zhangjian.3032 at bytedance.com>
Cc: Jeff9 Chan(陳松儉_ASRockRack) <Jeff9_Chan at asrockrack.com>; openbmc at lists.ozlabs.org
Subject: Re: [External] dbus-sensors issue

On Fri, Feb 07, 2025 at 07:54:28PM +0800, Jian Zhang wrote:
> See:
> https://lore.kernel.org/lkml/20230716195007.731909670@linuxfoundation.
> org/
> https://bugzilla.kernel.org/show_bug.cgi?id=217699
> For services utilizing io_uring, when waiting for I/O, CPU time is counted as I/O rather than idle time.

Yep.  So to be clear, this is just an accounting difference.  It has no real measurement of a performance difference.  "io_wait" is effectively "idle" now.

For similar reasons, phosphor-health-monitor doesn't consider 'iowait'
part of the CPU utilization for determining if the CPU has been too busy for too long:

https://github.com/openbmc/phosphor-health-monitor/blob/ba29dbdd04a96a46e1972641c20bf5a8e930ed8f/health_metric_collection.cpp#L73

> 
> Jian.
> > From: "Jeff9 Chan(陳松儉_ASRockRack)"<Jeff9_Chan at asrockrack.com>
> > Date:  Fri, Feb 7, 2025, 19:42
> > Subject:  [External] dbus-sensors issue
> > To: "openbmc at lists.ozlabs.org"<openbmc at lists.ozlabs.org>
> > Hi all,
> > It appears that IO wait is very high all the time. This can be 
> > viewed by running `top`. It was traced down to dbus-sensors systemd 
> > units. When the units are running, IO
>  wait is >90%. This can impact system performance and also impacts CPU utilization telemetry, since the idle task never runs, which normally means CPU is being completely utilized.
> >  
> > My platform uses below services, stop them will free the IO usage, any idea?
> >  
> > xyz.openbmc_project.hwmontempsensor.service
> > xyz.openbmc_project.fansensor.service
> > xyz.openbmc_project.adcsensor.service
> > xyz.openbmc_project.psusensor.service
> >  
> >  
> > best regards
> >  
> > Jeff Chan

--
Patrick Williams