Date:   Fri, 21 Jul 2017 17:21:31 +0000
From:   "Kani, Toshimitsu" <toshi.kani@....com>
To:     "mchehab@...pensource.com" <mchehab@...pensource.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "srinivas.pandruvada@...ux.intel.com" 
        <srinivas.pandruvada@...ux.intel.com>,
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        "tony.luck@...el.com" <tony.luck@...el.com>,
        "lenb@...nel.org" <lenb@...nel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>
Subject: Re: [PATCH 3/3] ghes_edac: add platform check to enable ghes_edac

On Fri, 2017-07-21 at 14:01 -0300, Mauro Carvalho Chehab wrote:
> Em Fri, 21 Jul 2017 16:40:20 +0000
> "Kani, Toshimitsu" <toshi.kani@....com> escreveu:
> 
> > On Fri, 2017-07-21 at 12:44 -0300, Mauro Carvalho Chehab wrote:
> > > Em Fri, 21 Jul 2017 15:34:50 +0000
> > > "Kani, Toshimitsu" <toshi.kani@....com> escreveu:
> > >   
> > > > On Fri, 2017-07-21 at 17:13 +0200, Borislav Petkov wrote:  
> > > > > On Fri, Jul 21, 2017 at 03:08:41PM +0000, Kani, Toshimitsu
> > > > > wrote:    
> > > > > > Yes, that is correct.  Corrected errors are reported to the
> > > > > > OS when they exceeded the platform's threshold.    
> > > > > 
> > > > > Are those thresholds user-configurable?    
> > > > 
> > > > I suppose it'd depend on vendors, but I do not think users can
> > > > do it properly unless they have depth knowledge about the
> > > > hardware.
> > > >   
> > > > > If not, what are you telling users who want to see *every*
> > > > > corrected error for measuring DIMM wear and so on...?    
> > > > 
> > > > Corrected errors are normal and expected to occur on healthy
> > > > hardware.  They do not need user's attention until they
> > > > repeatedly occurred at a same place.  
> > > 
> > > Yes, they're expected to happen. Still, some sys admins have
> > > their own measurements about what's "normal" for their scenario,
> > > and want to monitor every single corrected error, running their
> > > own algorithm to warn if the number of corrected errors is above
> > > their "normal" rate.  
> > 
> > I suppose these admins had to do it because their platforms
> > reported all corrected errors.  It addresses such administrators'
> > burden.
> 
> I see the value of having a threshold in BIOS, provided that it is
> well documented, and whose value can be adjusted, if needed.
> 
> One of the things I wanted to implement in ras-daemon were an
> algorithm that would be doing such threshold in software.
> The problem is that it would require field experience. So,
> I talked with a few vendors, to see if they could help doing
> it, but, on that time, none rised their hands :-)

I think it'd be very hard to keep it up to date.

> The thing with a BIOS threshold is that the user has no way to
> audit the algorithm. So, when BIOS start reporting such errors,
> it may be already too late: the systems may be in the verge of 
> losing data (or some data was already lost).
> 
> That's critical on cluster systems with thousands of machines:
> while the impact of disabling a cluster node to do some maintainance
> is marginal, the impact of an uncorrected error on a single
> machine may compromise weeks of expensive processing.
> 
> That's why some users prefer to monitor every single corrected
> error, and compare with the probability distribution they
> know that the risk of uncorrected errors is acceptable.

Right, I do not think all platforms need to be firmware-first.  I do
not want to talk like a sale's person, but we also offer lower-cost
platforms that do not come with built-in RAS.  Users can choose a right
model for their needs.

Thanks,
-Toshi

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