Re: [PATCH] EDAC: core EDAC support code

Doug Thompson
2006-03-10T00:52:25Z

On Fri, 2006-03-10 at 00:02 +0000, Greg KH wrote:
> On Thu, Mar 09, 2006 at 03:51:25PM -0800, Dave Peterson wrote:
> > On Tuesday 07 March 2006 11:03, Arjan van de Ven wrote:
> > > afaics it is a list of pci devices. these should just be symlinks to the
> > > sysfs resource of these pci devices instead, not a flat table file.
> >
> > Ok, I'm looking at the EDAC sysfs interface. I see the following
> > issues concerning the "one value per file" rule:
> >
> > 1. /sys/devices/system/edac/mc/mc0/module_name contains two
> > values, a module name and a version:
> >
> > # cat /sys/devices/system/edac/mc/mc0/module_name
> > k8_edac Ver: 2.0.1.devel Mar 8 2006
>
> Woah. That's what /sys/modules/ is for right? Don't add new stuff
> please.
>
> > 2. /sys/devices/system/edac/mc/mc0/supported_mem_type contains
> > the following on the machine I am looking at:
> >
> > # cat /sys/devices/system/edac/mc/mc0/supported_mem_type
> > Unbuffered-DDR Registered-DDR
> > #
> >
> > Here we have a whitespace-delimited list of values. Likewise,
> > the following files contain whitespace-delimited lists:
> >
> > /sys/devices/system/edac/mc/mc0/edac_capability
> > /sys/devices/system/edac/mc/mc0/edac_current_capability
>
> What exactly do they look like?

Unbuffered-DDR Registered-DDR

These come from the memory controller on what types of memory are
possible (or capable), NOT actuals. Its a domain of multiple types.

>
> > 3. The following files contain comma-delimited lists of
> > (vendor ID, device ID) tuples:
> >
> > /sys/devices/system/edac/pci/pci_parity_blacklist
> > /sys/devices/system/edac/pci/pci_parity_whitelist
>
> What exactly do they look like?

Example:

1022:7450,1434:16a6

is a list of 2 devices that should be skipped. Retrieved via a lspci.

PCI vendor-ID:device-ID series list. One or more devices are possible

The number of devices depends on how many devices should be skipped on a
given server.

Somehow the system admin needs to tell edac/pci to skip one or more
devices in the PCI device list. As the iterator proceeds through the PCI
device list, it compares each to a blacklist (or whitelist if on - only
one or the other can be one) entry. If found it skipsits. I toyed with
the idea of each PCI device having a control file and the admin setting
a scan/no-scan state, but quickly dropped that.

If a device is blacklisted, it is non-conforming to the PCI Parity
standard of operation and its status cannot be trusted. PCI-X Infiniband
card is such a card, though they have promised a firmware update.

>
> > I assume this is what Arjan is referring to.
> > Documentation/drivers/edac/edac.txt gives the following
> > description of how the whitelist functions:
> >
> > This control file allows for an explicit list of PCI
> > devices to be scanned for parity errors. Only devices
> > found on this list will be examined. The list is a line
> > of hexadecimel VENDOR and DEVICE ID tuples:
> >
> > 1022:7450,1434:16a6
> >
> > One or more can be inserted, seperated by a comma.
> > To write the above list doing the following as one
> > command line:
> >
> > echo "1022:7450,1434:16a6"
> > > /sys/devices/system/edac/pci/pci_parity_whitelist
> >
> > To display what the whitelist is, simply 'cat' the same
> > file.
> >
> > Looking at the current EDAC implementation, these are all of the
> > "one value per file" issues I see. If anyone sees any others I
> > missed, please let me know. Here are my thoughts on each:
> >
> > Issue #1
> > --------
> > Fixing this is easy. /sys/devices/system/edac/mc/mc0/module_name
> > can be replaced by two separate files, one providing the name and
> > the other providing the version:
> >
> > /sys/devices/system/edac/mc/mc0/module_name
> > /sys/devices/system/edac/mc/mc0/module_version
>
> No, these should just be deleted. Use the proper MODULE_* macros for
> these if you really want to display them to users.

When these macros are used, they then show up in the /sys/module/xxxx
directory, is that correct?

>
> > Issue #2
> > --------
> > To fix this, /sys/devices/system/edac/mc/mc0/supported_mem_type
> > can be made into a directory containing a file representing each
> > supported memory type. Thus we might have the following:
> >
> > /sys/devices/system/edac/mc/mc0/supported_mem_type
> > /sys/devices/system/edac/mc/mc0/supported_mem_type/Unbuffered-DDR
> > /sys/devices/system/edac/mc/mc0/supported_mem_type/Registered-DDR
> >
> > In the above example, the files Unbuffered-DDR and Registered-DDR
> > would each be empty in content. The presence of each file would
> > indicate that the memory type it represents is supported.

This attribute reports POSSIBLE memory types, not ACTUAL memory type.

>
> I don't think the original file is really a big problem.

Are you saying to leave it as is?

the supported_mem_type reports what the memory controller is CAPABLE of
supporting. Then in '..../mc0/csrowN/mem_type' reports what is ACTUALLY
being used.

>
> > Issue #3
> > --------
> > I am unclear about what to do here. If the list contents were
> > read-only, it would be relatively easy to make
> > /sys/devices/system/edac/pci/pci_parity_whitelist into a directory
> > containing symlinks, one for each device. However, the user is
> > supposed to be able to modify the list contents. This would imply
> > that the user creates and destroys symlinks. Does sysfs currently
> > support this sort of behavior? If not, what is the preferred
> > means for implementing a user-modifiable set of values?

This input and presentation of a list was troublesome in matching the
one attribute policy.

>
> No it doesn't. How big can this list get?

Depends on how many PCI devices there are AND which ones have been
identified as non-conforming to the PCI standard for PCI parity status.

At most, the Number of devices minus 1, but then using a 'whitelist'
with just that one lone device would be better. IF all devices are
listed in a blacklist, then just turn off parity checking instead.

Getting the blacklist/whitelist into the edac driver took some pondering
and various designs on my part. I might have missed a more obvious
solution.

>
> thanks,
>
> greg k-h

thanks

doug t