linux-kernel - Re: k10temp: ZEN3 readings are broken

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Date:   Wed, 23 Dec 2020 12:27:31 +0100
From:   Gabriel C <nix.or.die@...glemail.com>
To:     Jan Engelhardt <jengelh@...i.de>
Cc:     Guenter Roeck <linux@...ck-us.net>, linux-hwmon@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Wei Huang <wei.huang2@....com>
Subject: Re: k10temp: ZEN3 readings are broken

Am Mi., 23. Dez. 2020 um 11:41 Uhr schrieb Jan Engelhardt <jengelh@...i.de>:
>
>
> On Tuesday 2020-12-22 04:58, Guenter Roeck wrote:
> >On 12/21/20 5:45 PM, Gabriel C wrote:
> >> Hello Guenter,
> >>
> >> while trying to add ZEN3 support for zenpower out of tree modules, I find out
> >> the in-kernel k10temp driver is broken with ZEN3 ( and partially ZEN2 even ).
> >
> >[...] since I do not have time to actively maintain
> >the driver, since each chip variant seems to use different addresses and scales,
> >and since the information about voltages and currents is unpublished by AMD,
> >I'll remove support for voltage/current readings from the upstream driver.
>
> I support that decision.
>
> /proc/cpuinfo::AMD Ryzen 7 3700X 8-Core Processor, fam 23 model 113 step 0
>
> A synthetic load (perl -e '1 while 1') x 16 shows:
> Adapter: PCI adapter
> Vcore:        +1.28 V
> Vsoc:         +1.02 V
> Tctl:         +94.8°C
> Tdie:         +94.8°C
> Tccd1:        +94.8°C
> Icore:       +76.00 A
> Isoc:         +6.75 A
>
> A BOINC workload on average:
> k10temp-pci-00c3
> Adapter: PCI adapter
> Vcore:        +1.17 V
> Vsoc:         +1.02 V
> Tctl:         +94.9°C
> Tdie:         +94.9°C
> Tccd1:        +95.0°C
> Icore:       +88.00 A
> Isoc:         +8.00 A
>
> The BOINC workload, when it momentarily spikes:
> Adapter: PCI adapter
> Vcore:        +1.32 V
> Vsoc:         +1.02 V
> Tctl:         +94.1°C
> Tdie:         +94.1°C
> Tccd1:        +96.0°C
> Icore:       +105.00 A
> Isoc:         +7.75 A
>
> For a processor sold as a 65 W part, observing reported sensors as
> 88 A x 1.17 V + 8 A x 1.02 V = 111.12 W just can't be. We are off by a
> factor of about 2.

Just before I forget, even with 100% correct code you could still be off by
a factor of 2 with a broken BIOS or a vendor who is trying to bypass AMD
spec limits.

See as an example this topic:
https://cutt.ly/7h1bT48

Best Regards,

Gabriel C