In case of partial hit WO engine first reads data for the entire
request address range from core device. Then it plumbs it by fetching
dirty sectors from cache device.
For unindentified reason this leads to a data corruption in YCSB
workload A. After flushing dirty data and re-loading cache the
data is correct.
This change modifies WO read handler to read clean data from the
cache. This is not optimal, as the clean sectors are now read twice
in case of partial hit. For now it seems to be good enough work-around
for the data corruption problem.
The symptoms, combined with the fact that this change seems to make
the problem go away, indicates that at some point WB write handler
(and/or special I/O request handlers like discard) puts CAS in a
state where in-memory medata wrongly indicates that a sector is
clean while in fact it is dirty, as marked in the on-disk metadata.
Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>
This change introduced a race condition. In some code paths after
cacheline trylock failed, hash bucket lock needed bo be upgraded
in order to obtain asynchronous lock. During hash bucket lock
upgrade, hash read locks were released followed by obtaining
hash write locks. After read locks were released, concurrent
thread could obtain hash bucket locks and modify cacheline
state. The thread upgrading hash bucket lock would need to
repeat traversation in order to safely continue.
This reverts commit 30f22d4f47.
Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>
Hash bucket read/write lock is sufficient to safely attempt
cacheline trylock/lock. This change removes cacheline lock
global RW semaprhore and moves cacheline trylock/lock under
hash bucket read/write lock respectively.
Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>
WO cache mode should not repartition cachelines nor affect cacheline
status in any way when servicing read. Reading data from the cache
is just an internal optimization. Also WO cache mode is designed to
be used with partitioning based on write life-time hints and read
requests do not carry write lifetime hint by definition.
Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>
Static code analyzers fail to understand that this variable
is always assigned to before usage.
Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>
Write-only cache mode is similar to writeback, however read
operations do not promote data to cache. Reads are mostly serviced
by the core device, only dirty sectors are fetched from the cache.
Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>
