Details:
- Defined a new struct datatype, rntm_t (runtime), to house the thrloop
field of the cntx_t (context). The thrloop array holds the number of
ways of parallelism (thread "splits") to extract per level-3
algorithmic loop until those values can be used to create a
corresponding node in the thread control tree (thrinfo_t structure),
which (for any given level-3 invocation) usually happens by the time
the macrokernel is called for the first time.
- Relocating the thrloop from the cntx_t remedies a thread-safety issue
when invoking level-3 operations from two or more application threads.
The race condition existed because the cntx_t, a pointer to which is
usually queried from the global kernel structure (gks), is supposed to
be a read-only. However, the previous code would write to the cntx_t's
thrloop field *after* it had been queried, thus violating its read-only
status. In practice, this would not cause a problem when a sequential
application made a multithreaded call to BLIS, nor when two or more
application threads used the same parallelization scheme when calling
BLIS, because in either case all application theads would be using
the same ways of parallelism for each loop. The true effects of the
race condition were limited to situations where two or more application
theads used *different* parallelization schemes for any given level-3
call.
- In remedying the above race condition, the application or calling
library can now specify the parallelization scheme on a per-call basis.
All that is required is that the thread encode its request for
parallelism into the rntm_t struct prior to passing the address of the
rntm_t to one of the expert interfaces of either the typed or object
APIs. This allows, for example, one application thread to extract 4-way
parallelism from a call to gemm while another application thread
requests 2-way parallelism. Or, two threads could each request 4-way
parallelism, but from different loops.
- A rntm_t* parameter has been added to the function signatures of most
of the level-3 implementation stack (with the most notable exception
being packm) as well as all level-1v, -1d, -1f, -1m, and -2 expert
APIs. (A few internal functions gained the rntm_t* parameter even
though they currently have no use for it, such as bli_l3_packm().)
This required some internal calls to some of those functions to
be updated since BLIS was already using those operations internally
via the expert interfaces. For situations where a rntm_t object is
not available, such as within packm/unpackm implementations, NULL is
passed in to the relevant expert interfaces. This is acceptable for
now since parallelism is not obtained for non-level-3 operations.
- Revamped how global parallelism is encoded. First, the conventional
environment variables such as BLIS_NUM_THREADS and BLIS_*_NT are only
read once, at library initialization. (Thanks to Nathaniel Smith for
suggesting this to avoid repeated calls getenv(), which can be slow.)
Those values are recorded to a global rntm_t object. Public APIs, in
bli_thread.c, are still available to get/set these values from the
global rntm_t, though now the "set" functions have additional logic
to ensure that the values are set in a synchronous manner via a mutex.
If/when NULL is passed into an expert API (meaning the user opted to
not provide a custom rntm_t), the values from the global rntm_t are
copied to a local rntm_t, which is then passed down the function stack.
Calling a basic API is equivalent to calling the expert APIs with NULL
for the cntx and rntm parameters, which means the semantic behavior of
these basic APIs (vis-a-vis multithreading) is unchanged from before.
- Renamed bli_cntx_set_thrloop_from_env() to bli_rntm_set_ways_for_op()
and reimplemented, with the function now being able to treat the
incoming rntm_t in a manner agnostic to its origin--whether it came
from the application or is an internal copy of the global rntm_t.
- Removed various global runtime APIs for setting the number of ways of
parallelism for individual loops (e.g. bli_thread_set_*_nt()) as well
as the corresponding "get" functions. The new model simplifies these
interfaces so that one must either set the total number of threads, OR
set all of the ways of parallelism for each loop simultaneously (in a
single function call).
- Updated sandbox/ref99 according to above changes.
- Rewrote/augmented docs/Multithreading.md to document the three methods
(and two specific ways within each method) of requesting parallelism
in BLIS.
- Removed old, disabled code from bli_l3_thrinfo.c.
- Whitespace changes to code (e.g. bli_obj.c) and docs/BuildSystem.md.
Details:
- Applied changes to ref99 sandbox analagous to those applied to
framework code in f97a86f. This involves setting the pack schemas of
A and B objects temporarily to communicate those desired schemas to
the control tree creation function in blx_gemm_cntl.c. This allows us
to (henceforth) query the schemas from the control tree rather than
the context.
Details:
- Changed the way virtual microkernels are handled in the context.
Previously, there were query routines such as bli_cntx_get_l3_ukr_dt()
which returned the native ukernel for a datatype if the method was
equal to BLIS_NAT, or the virtual ukernel for that datatype if the
method was some other value. Going forward, the context native and
virtual ukernel slots will both be initialized to native ukernel
function pointers for native execution, and for non-native execution
the virtual ukernel pointer will be something else. This allows us
to always query the virtual ukernel slot (from within, say, the
macrokernel) without needing any logic in the query routine to decide
which function pointer (native or virtual) to return. (Essentially,
the logic has been shifted to init-time instead of compute-time.)
This scheme will also allow generalized virtual ukernels as a way
to insert extra logic in between the macrokernel and the native
microkernel.
- Initialize native contexts (in bli_cntx_ref.c) with native ukernel
function addresses stored to the virtual ukernel slots pursuant to
the above policy change.
- Renamed all static functions that were native/virtual-ambiguous, such
as bli_cntx_get_l3_ukr_dt() or bli_cntx_l3_ukr_prefers_cols_dt()
pursuant to the above polilcy change. Those routines now use the
substring "get_l3_vir_ukr" in their name instead of "get_l3_ukr". All
of these functions were static functions defined in bli_cntx.h, and
most uses were in level-3 front-ends and macrokernels.
- Deprecated anti_pref bool_t in context, along with related functions
such as bli_cntx_l3_ukr_eff_dislikes_storage_of(), now that 1m's
panel-block execution is disabled.
Details:
- Reordered the arguments in the ref99 sandbox's call to
bli_cntx_set_thrloop_from_env() to be consistent with the updated
function signature from f97a86f. Thanks to Devangi Parikh for
reporting this issue.
Details:
- Minor edits to sandbox/ref99/README.md.
- Removed cpp guards in sandbox/ref99/thread/blx_gemm_thread.h to be
consistent with other headers in sandbox/ref99.
- Additional targets and related cleanups in test/3m4m/Makefile.
Details:
- Renamed sandbox/c99 to sandbox/ref99. I wanted to name the sandbox so
that it would be thought of as a "reference" sandbox. I kept the "99"
to differientiate it from future reference sandboxes that may be
written in another language (such as C++).
- Updates to sandbox/ref99/README.md.
