Re: Request for Feedback :: Time Mode setting in timemanager

From: Patrick Williams <patrick@stwcx.xyz>
To: Brad Bishop <bradleyb@fuzziesquirrel.com>
Cc: Vishwanatha Subbanna <vishwa@linux.vnet.ibm.com>,
	"openbmc@lists.ozlabs.org" <openbmc@lists.ozlabs.org>
Subject: Re: Request for Feedback :: Time Mode setting in timemanager
Date: Tue, 18 Feb 2020 14:25:07 -0600	[thread overview]
Message-ID: <20200218202507.GA2219@patrickw3-mbp.lan.stwcx.xyz> (raw)
In-Reply-To: <5B7FD9A0-8A4A-4BCC-9BC5-77B5DEBCDD00@fuzziesquirrel.com>

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On Tue, Feb 18, 2020 at 09:40:53AM -0500, Brad Bishop wrote:
> 
> 
> > On Feb 18, 2020, at 7:56 AM, Vishwanatha Subbanna <vishwa@linux.vnet.ibm.com> wrote:
> > However, if the user changes the setting when the Host is booting, timemanager puts them in deferred state. Meaning, timemanager does not take the settings into effect until the Host is powered off.
> 
> Can you elaborate on why it does this?
> 
> > 
> > So, if someone wants to move from [Manual] to [NTP] or vice-versa, when the Host is [On], they need to [power-off] the Host and power it back on.
> 
> This seems less than ideal?  Would you agree?
> 
> > 
> > This design was chosen because we wanted to give priority to Host.
> 
> What does it mean to give priority to the Host?  Are you trying to hide time changes in the time from the host?  Why?
> 
> > Some of us are asking me if we can make a change to take the setting changes in effect immediately, not caring the state of the Host.
> 
> Without additional background this is what seems intuitive to me.
> 

Most of these design points came from considering how it might be best
for a cloud provider, like Rackspace, we were originally designing some
of this code for.

If I'm leasing the host processor from you, I don't necessarily trust
your time infrastructure and might want to use my own.  A compromised
time infrastructure can be used to get you to use expired SSL
certificates, for example.

With this in mind came all of these design points of "the host has
priority", "you may not change modes out from underneath a running host",
etc.

> > 
> > Please could you help with your thoughts on this ?.. What is the Industry norm on this ?
> 
> FWIW on our (IBM) system designs we usually hook an RTC up to the BMC, and any host software needing a RTC has to get it via some in-band software interface.  I think I heard somewhere though that often in other systems designs the RTC is connected to the host processors and the BMC doesn’t have access to it.

FB's OCP designs all have the RTC to the Host, so I'm not sure any of
this is applicable to us.

-- 
Patrick Williams

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