Split traversation into two distinct phases: lookup()
and lru set_hot(). prepare_cachelines() now only calls
set_hot() once after lookup and insert are finished.
lookup() is called explicitly only once in
prepare_cachelines() at the very beginning of the
procedure. If request is a miss then then map()
performs operations equivalent to lookup() supplemented
by an attempt to map cachelines. Both lookup() and
set_hot() are called via traverse() from the engines
which do not attempt mapping, and thus do not call
prepare_clines().
Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>
Allowing request cacheline lock to be called on partially
locked request. This is going to be usefull for upcomming
eviction improvements, where request will first have evicted
(LOOKUP_REMAPPED) cachelines assigned to it in a locked state,
followed by standard request cacheline lock call in order to
lock previously inserted (LOOKUP_HIT) or mapped from freelist
(LOOKUP_INSERTED) cachelines.
Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>
Function returns true if cacheline is locked (read
or write) by exactly one entity with no waiters.
This is usefull for eviction. Assuming caller holds
hash bucket write lock, having exlusive cacheline
lock (either read or write) allows holder to remap
cacheline safely. Typically during eviction hash
bucket is unknown until resolved under cacheline lock,
so locking cacheline exclusively (instead of locking
and checking for exclusive lock) is not possible.
More specifically this is the flow for synchronizing
cacheline remap using ocf_cache_line_is_locked_exclusively:
1. acquire a cacheline (read or write) lock
2. resolve hash bucket
3. write-lock hash bucket
4. verify cacheline lock is exclusive
Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>
Provide number of cachelines as the cacheline concurrency
construtor param instead of reading it from cache.
The purpose of this change is to improve testability.
Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>
Cacheline concurrency functions have their interface changed
so that the cacheline concurrency private context is
explicitly on the parameter list, rather than being taken
from cache->device->concurrency.cache_line.
Cache pointer is no longer provided as a parameter to these
functions. Cacheline concurrency context now has a pointer
to cache structure (for logging purposes only).
The purpose of this change is to facilitate unit testing.
Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>
The main purpose of cacheline concurrency global lock
is to eliminate the possibility of deadlocks when
locking multiple cachelines.
Cacheline lock fast path does not need to acquire
this lock, as it is only opportunistically attempting
to lock all clines without wait. There is no risk
of deadlock, as:
* concurrent fast path will also only try_lock
cachelines, releasing all acquired locks if failed
to immediately acquire lock for any cacheline
* concurrent slow path is guaranteed to have
precedence in lock acquisition when conditions
for deadlock occure (both slowpath and fastpath
have acquired some locks required by the other
thread). This is because the fastpath thread will
back off (release acquired locks) if any one of the
cacheline locks is not acquired.
Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>
.. in order to move primitives intended to be accessed
concurrently in separate CPU cache line.
Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>
Divide single global lock instance into 4 to reduce contention
in multiple read-locks scenario.
Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>
1. new abbreviated previx: ocf_hb (HB stands for hash bucket)
2. clear distinction between functions requiring caller to
hold metadata shared global lock ("naked") vs the ones
which acquire global lock on its own ("prot" for protected)
3. clear distinction between hash bucket locking functions
accepting hash bucket id ("id"), core line and lba ("cline")
and entire request ("req").
Resulting naming scheme:
ocf_hb_(id/cline/req)_(prot/naked)_(lock/unlock/trylock)_(rd/wr)
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>
Adding locks to assure partition list consistency. Partition
lists is typically modified under cacheline or hash bucket lock.
This is not sufficient synchronization as adding/removing cacheline
from partition list affects neighbouring cachelines state as well.
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>
There is one RW lock per hash bucket. Write lock is required
to map cacheline, read lock is sufficient for traversing.
Hash bucket locks are always acquired under global metadata
read lock. This assures mutual exclusion with eviction and
management paths, where global metadata write lock is held.
Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>
This change refactors the code in order to prepare for removing
global concurrency lock, which won't be needed after per-bucket
metadata locking is in place.
Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>
Environment should provide calls for destroying primitives (i.e. env_mutex_destroy()) and OCF should call these functions in its cleanup paths.
Signed-off-by: Firas Medini <mdnfiras@yahoo.com>
