On XO-1.5 with 11.3.0/11.3.1 -- hang during shutdown?

James Cameron quozl at laptop.org
Sun Jun 17 19:49:41 EDT 2012

On Sat, Jun 16, 2012 at 01:44:23AM -0700, John Gilmore wrote:
> I doubt that this issue is your problem.  But in response to one remark:
> >                                  On the theory that these writes may
> > be stalling due to the block number, (and we haven't seen any evidence
> > yet of this), you can test for that by repeating the writes...
> There *is* evidence that accesses to some block numbers in MLC flash
> chips are much faster or slower than others (like 5x slower).  They
> seem to be designed with "fast blocks" and "slow blocks", though this
> is undocumented.  There is no interface for telling the software
> which is which (except by actual measurement of the responsiveness of
> the chip -- and in microSD cards, accesses are mediated by a Flash
> Translation Layer of unknown characteristics).  [...]

Indeed.  We have no clue what the FTL is doing, and can only probe it
from the outside by timing operations using the virtual block numbers.

I think that would be useful testing: (a) does the read or write
timing vary, and (b) do any operation stall for the period the hang is

I agree that this is unlikely to be the problem, and it would be
better to find out what the kernel is doing at the time of the hang.

Thanks for the paper links.

James Cameron

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