diff options
Diffstat (limited to 'Documentation/nvdimm/btt.txt')
| -rw-r--r-- | Documentation/nvdimm/btt.txt | 24 |
1 files changed, 17 insertions, 7 deletions
diff --git a/Documentation/nvdimm/btt.txt b/Documentation/nvdimm/btt.txt index 95134d5ec4a0..b91443f577dc 100644 --- a/Documentation/nvdimm/btt.txt +++ b/Documentation/nvdimm/btt.txt @@ -80,9 +80,17 @@ block. Each map entry is 32 bits. The two most significant bits are special flags, and the remaining form the internal block number. Bit Description -31 : TRIM flag - marks if the block was trimmed or discarded -30 : ERROR flag - marks an error block. Cleared on write. -29 - 0 : Mappings to internal 'postmap' blocks +31 - 30 : Error and Zero flags - Used in the following way: + Bit Description + 31 30 + ----------------------------------------------------------------------- + 00 Initial state. Reads return zeroes; Premap = Postmap + 01 Zero state: Reads return zeroes + 10 Error state: Reads fail; Writes clear 'E' bit + 11 Normal Block – has valid postmap + + +29 - 0 : Mappings to internal 'postmap' blocks Some of the terminology that will be subsequently used: @@ -127,10 +135,11 @@ old_map': alternate old postmap entry new_map': alternate new postmap entry seq' : alternate sequence number. -Each of the above fields is 32-bit, making one entry 16 bytes. Flog updates are +Each of the above fields is 32-bit, making one entry 32 bytes. Entries are also +padded to 64 bytes to avoid cache line sharing or aliasing. Flog updates are done such that for any entry being written, it: a. overwrites the 'old' section in the entry based on sequence numbers -b. writes the new entry such that the sequence number is written last. +b. writes the 'new' section such that the sequence number is written last. c. The concept of lanes @@ -141,8 +150,9 @@ concurrently, 'nlanes' is the number of IOs the BTT device as a whole can process. nlanes = min(nfree, num_cpus) A lane number is obtained at the start of any IO, and is used for indexing into -all the on-disk and in-memory data structures for the duration of the IO. It is -protected by a spinlock. +all the on-disk and in-memory data structures for the duration of the IO. If +there are more CPUs than the max number of available lanes, than lanes are +protected by spinlocks. d. In-memory data structure: Read Tracking Table (RTT) |