Details:
- trsm parallelization was temporarily simplifed in 075143d to entirely
ignore any parallelism specified via the pc or ir loops. Now, any
parallelism specified to the pc loop will be redirected to the ic
loop, and any parallelism specified to the ir loop will be redirected
to the jr loop. (Note that because of inter-iteration dependencies,
trsm cannot parallelize the ir loop. Parallelism via the pc loop is
at least somewhat feasible in theory, but it would require tracking
dependencies between blocks--something for which BLIS currently lacks
the necessary supporting infrastructure.)
Details:
- Parallelism within the IC loop (3rd loop around the microkernel) is
now supported within the trsm operation. This is done via a new branch
on each of the control and thread trees, which guide execution of a
new trsm-only subproblem from within bli_trsm_blk_var1(). This trsm
subproblem corresponds to the macrokernel computation on only the
block of A that contains the diagonal (labeled as A11 in algorithms
with FLAME-like partitioning), and the corresponding row panel of C.
During the trsm subproblem, all threads within the JC communicator
participate and parallelize along the JR loop, including any
parallelism that was specified for the IC loop. (IR loop parallelism
is not supported for trsm due to inter-iteration dependencies.) After
this trsm subproblem is complete, a barrier synchronizes all
participating threads and then they proceed to apply the prescribed
BLIS_IC_NT (or equivalent) ways of parallelism (and any BLIS_JR_NT
parallelism specified within) to the remaining gemm subproblem (the
rank-k update that is performed using the newly updated row-panel of
B). Thus, trsm now supports JC, IC, and JR loop parallelism.
- Modified bli_trsm_l_cntl_create() to create the new "prenode" branch
of the trsm_l cntl_t tree. The trsm_r tree was left unchanged, for
now, since it is not currently used. (All trsm problems are cast in
terms of left-side trsm.)
- Updated bli_cntl_free_w_thrinfo() to be able to free the newly shaped
trsm cntl_t trees. Fixed a potentially latent bug whereby a cntl_t
subnode is only recursed upon if there existed a corresponding
thrinfo_t node, which may not always exist (for problems too small
to employ full parallelization due to the minimum granularity imposed
by micropanels).
- Updated other functions in frame/base/bli_cntl.c, such as
bli_cntl_copy() and bli_cntl_mark_family(), to recurse on sub-prenodes
if they exist.
- Updated bli_thrinfo_free() to recurse into sub-nodes and prenodes
when they exist, and added support for growing a prenode branch to
bli_thrinfo_grow() via a corresponding set of help functions named
with the _prenode() suffix.
- Added a bszid_t field thrinfo_t nodes. This field comes in handy when
debugging the allocation/release of thrinfo_t nodes, as it helps trace
the "identity" of each nodes as it is created/destroyed.
- Renamed
bli_l3_thrinfo_print_paths() -> bli_l3_thrinfo_print_gemm_paths()
and created a separate bli_l3_thrinfo_print_trsm_paths() function to
print out the newly reconfigured thrinfo_t trees for the trsm
operation.
- Trival changes to bli_gemm_blk_var?.c and bli_trsm_blk_var?.c
regarding variable declarations.
- Removed subpart_t enum values BLIS_SUBPART1T, BLIS_SUBPART1B,
BLIS_SUBPART1L, BLIS_SUBPART1R. Then added support for two new labels
(semantically speaking): BLIS_SUBPART1A and BLIS_SUBPART1B, which
represent the subpartition ahead of and behind, respectively,
BLIS_SUBPART1. Updated check functions in bli_check.c accordingly.
- Shuffled layering/APIs for bli_acquire_mpart_[mn]dim() and
bli_acquire_mpart_t2b/b2t(), _l2r/r2l().
- Deprecated old functions in frame/3/bli_l3_thrinfo.c.
Details:
- Removed explicit reference to The University of Texas at Austin in the
third clause of the license comment blocks of all relevant files and
replaced it with a more all-encompassing "copyright holder(s)".
- Removed duplicate words ("derived") from a few kernels' license
comment blocks.
- Homogenized license comment block in kernels/zen/3/bli_gemm_small.c
with format of all other comment blocks.
Details:
- Renamed the following C preprocessor macros whose fallback/default
values are specified within frame/include/bli_kernel_macro_defs.h:
BLIS_DEFAULT_MR_THREAD_MAX -> BLIS_THREAD_MAX_IR
BLIS_DEFAULT_NR_THREAD_MAX -> BLIS_THREAD_MAX_JR
BLIS_DEFAULT_M_THREAD_RATIO -> BLIS_THREAD_RATIO_M
BLIS_DEFAULT_N_THREAD_RATIO -> BLIS_THREAD_RATIO_N
- Renamed the above cpp macro overrides within the knl, skx, and zen
sub-configurations, as well as invocations of those macros in
bli_rntm.c.
- Moved config/zen/bli_kernel.h to an 'old' directory as it is no longer
used by any code within BLIS.
Details:
- Previously, trsm was consolidating all ways of parallelism into the jr
loop. This was unnecessary and to some degree detrimental on some
types of hardware. Now, any parallelism bound for the jc loop will be
applied to the jc loop, while all other loops' parallelism is funneled
to the jr loop. Thanks to Devangi Parikh for helping investigate this
issue and suggesting the fix.
- NOTE: This change affects only left-side trsm. However, currently
right-side trsm is currently implemented in terms of the left-side
case, and thus the change effectively applies to both left and right
cases.
Details:
- Removed four trailing spaces after "BLIS" that occurs in most files'
commented-out license headers.
- Added UT copyright lines to some files. (These files previously had
only AMD copyright lines but were contributed to by both UT and AMD.)
- In some files' copyright lines, expanded 'The University of Texas' to
'The University of Texas at Austin'.
- Fixed various typos/misspellings in some license headers.
Details:
- Fixed an unused variable warning in frame/base/bli_rntm.c when
multithreading is disabled.
- Fixed a missing variable declaration in bli_thread_init_rntm_from_env()
when multithreading is disabled.
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.
