netdev - RE: [PATCH v0 03/12] mlxsw: core: Add core environment module for port temperature reading

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Date:   Thu, 21 Jun 2018 18:14:43 +0000
From:   Vadim Pasternak <vadimp@...lanox.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "jiri@...nulli.us" <jiri@...nulli.us>
Subject: RE: [PATCH v0 03/12] mlxsw: core: Add core environment module for
 port temperature reading

> -----Original Message-----
> From: Andrew Lunn [mailto:andrew@...n.ch]
> Sent: Thursday, June 21, 2018 8:11 PM
> To: Vadim Pasternak <vadimp@...lanox.com>
> Cc: davem@...emloft.net; netdev@...r.kernel.org; jiri@...nulli.us
> Subject: Re: [PATCH v0 03/12] mlxsw: core: Add core environment module for
> port temperature reading
> 
> > New internal API reads the temperature from all the modules, which are
> > equipped with the thermal sensor and exposes temperature according to
> > the worst measure. All individual temperature values are normalized to
> > pre-defined range.
> 
> Hi Vadim
> 
> Could you explain this normalization process. Why are you not just expose each
> sensors temperature in millidegrees C, which is the normal for HWMON.

Hi Andrew,

The temperature of each individual module can be obtained
through ethtool.
The worst temperature is necessary for the system cooling
control decision.

Up to 64 SFP/QSFP modules could be connected to the system.
Some of them could cooper modules, which doesn't provide
temperature measurement.
Some of them could be optical modules, providing untrusted
temperature measurement, which could impact thermal
control of the system.
Also optical modules could be from the different vendors,  and
this is real situation, when, f.e. one module has the warning and
critical thresholds 75C and 85C, while another 70C and 80C.
In such case  the first module temperature 72C is better, then the
second module temperature 71C.

And deltas  between warning and critical thresholds, could be
different as well. It could be 5C, 10C, etc.  

So, nominal temperature is not the case here, we should know the
"worst" value for the thermal control decision.

Thanks,
Vadim.

> 
>     Andrew