18 Jun, 2016
1 commit
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Section 5 about BTT's in kernel usage was quite obsolete,
replace it with a simple 'Usage' section that describes how
to set up a BTT namespace using the 'ndctl' utility.Signed-off-by: Vishal Verma
Signed-off-by: Dan Williams
13 Nov, 2015
1 commit
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A bunch of changes that I hope will help in understanding it
better for first-time readers.Signed-off-by: Konrad Rzeszutek Wilk
Signed-off-by: Dan Williams
26 Jun, 2015
2 commits
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Maintainer information and documentation for drivers/nvdimm
Cc: Andy Lutomirski
Cc: Boaz Harrosh
Cc: H. Peter Anvin
Cc: Jens Axboe
Cc: Ingo Molnar
Cc: Christoph Hellwig
Cc: Neil Brown
Cc: Greg KH
Signed-off-by: Dan Williams -
BTT stands for Block Translation Table, and is a way to provide power
fail sector atomicity semantics for block devices that have the ability
to perform byte granularity IO. It relies on the capability of libnvdimm
namespace devices to do byte aligned IO.The BTT works as a stacked blocked device, and reserves a chunk of space
from the backing device for its accounting metadata. It is a bio-based
driver because all IO is done synchronously, and there is no queuing or
asynchronous completions at either the device or the driver level.The BTT uses 'lanes' to index into various 'on-disk' data structures,
and lanes also act as a synchronization mechanism in case there are more
CPUs than available lanes. We did a comparison between two lane lock
strategies - first where we kept an atomic counter around that tracked
which was the last lane that was used, and 'our' lane was determined by
atomically incrementing that. That way, for the nr_cpus > nr_lanes case,
theoretically, no CPU would be blocked waiting for a lane. The other
strategy was to use the cpu number we're scheduled on to and hash it to
a lane number. Theoretically, this could block an IO that could've
otherwise run using a different, free lane. But some fio workloads
showed that the direct cpu -> lane hash performed faster than tracking
'last lane' - my reasoning is the cache thrash caused by moving the
atomic variable made that approach slower than simply waiting out the
in-progress IO. This supports the conclusion that the driver can be a
very simple bio-based one that does synchronous IOs instead of queuing.Cc: Andy Lutomirski
Cc: Boaz Harrosh
Cc: H. Peter Anvin
Cc: Jens Axboe
Cc: Ingo Molnar
Cc: Christoph Hellwig
Cc: Neil Brown
Cc: Jeff Moyer
Cc: Dave Chinner
Cc: Greg KH
[jmoyer: fix nmi watchdog timeout in btt_map_init]
[jmoyer: move btt initialization to module load path]
[jmoyer: fix memory leak in the btt initialization path]
[jmoyer: Don't overwrite corrupted arenas]
Signed-off-by: Vishal Verma
Signed-off-by: Dan Williams
