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No longer need them as temp vars in the cmm primop implementations.
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This reduces the latency between a context-switch being triggered and
the thread returning to the scheduler, which in turn should reduce the
cost of the GC barrier when there are many cores.
We still retain the old context_switch flag which is checked at the
end of each block of allocation. The idea is that setting HpLim may
fail if the the target thread is modifying HpLim at the same time; the
context_switch flag is a fallback. It also allows us to "context
switch soon" without forcing an immediate switch, which can be costly.
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Fixes crashes on Windows and Sparc
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Eager blackholing can improve parallel performance by reducing the
chances that two threads perform the same computation. However, it
has a cost: one extra memory write per thunk entry.
To get the best results, any code which may be executed in parallel
should be compiled with eager blackholing turned on. But since
there's a cost for sequential code, we make it optional and turn it on
for the parallel package only. It might be a good idea to compile
applications (or modules) with parallel code in with
-feager-blackholing.
ToDo: document -feager-blackholing.
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Spark stealing support for PARALLEL_HASKELL and THREADED_RTS versions of the RTS.
Spark pools are per capability, separately allocated and held in the Capability
structure. The implementation uses Double-Ended Queues (deque) and cas-protected
access.
The write end of the queue (position bottom) can only be used with
mutual exclusion, i.e. by exactly one caller at a time.
Multiple readers can steal()/findSpark() from the read end
(position top), and are synchronised without a lock, based on a cas
of the top position. One reader wins, the others return NULL for a
failure.
Work stealing is called when Capabilities find no other work (inside yieldCapability),
and tries all capabilities 0..n-1 twice, unless a theft succeeds.
Inside schedulePushWork, all considered cap.s (those which were idle and could
be grabbed) are woken up. Future versions should wake up capabilities immediately when
putting a new spark in the local pool, from newSpark().
Patch has been re-recorded due to conflicting bugfixes in the sparks.c, also fixing a
(strange) conflict in the scheduler.
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This has several advantages:
- -fvia-C is consistent with -fasm with respect to FFI declarations:
both bind to the ABI, not the API.
- foreign calls can now be inlined freely across module boundaries, since
a header file is not required when compiling the call.
- bootstrapping via C will be more reliable, because this difference
in behavour between the two backends has been removed.
There is one disadvantage:
- we get no checking by the C compiler that the FFI declaration
is correct.
So now, the c-includes field in a .cabal file is always ignored by
GHC, as are header files specified in an FFI declaration. This was
previously the case only for -fasm compilations, now it is also the
case for -fvia-C too.
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ghc fails to build if you use an external gmp library. This is because
ghc requires the header file gmp.h, which used to be provided by the
internal gmp source code. The file gmp.h is no longer part of the
gmp source code, but is generated as part of the build procedure.
If an external gmp is specified, the internal gmp is not build and the
gmp.h file never gets generated.
Of course, it was a bad idea anyway to use a header file from a potentially
different version of the library.
The patch sets HAVE_LIB_GMP if the gmp library is found during configuration
and conditionalizes including the library header file on it.
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On OS X, we have to #include <GMP/gmp.h> if we are using GMP.framework. Before
the recent GMP changes, gcc (incorrectly) used the gmp.h supplied by ghc but
that is gone now.
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so that we can calculate deterministic offsets to some of the fields
of Capability.
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Most of the other users of the fptools build system have migrated to
Cabal, and with the move to darcs we can now flatten the source tree
without losing history, so here goes.
The main change is that the ghc/ subdir is gone, and most of what it
contained is now at the top level. The build system now makes no
pretense at being multi-project, it is just the GHC build system.
No doubt this will break many things, and there will be a period of
instability while we fix the dependencies. A straightforward build
should work, but I haven't yet fixed binary/source distributions.
Changes to the Building Guide will follow, too.
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