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author | Torbjorn Granlund <tege@gmplib.org> | 2011-11-24 12:39:37 +0100 |
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committer | Torbjorn Granlund <tege@gmplib.org> | 2011-11-24 12:39:37 +0100 |
commit | 52b003cc5830e7fde5e3dca4338c170f3cdd9fe5 (patch) | |
tree | c39bf8d7a297f9e5f23ed8280111fa40b342e548 | |
parent | 161de004453f214c6030bb9e9babd2d0048a7337 (diff) | |
download | gmp-52b003cc5830e7fde5e3dca4338c170f3cdd9fe5.tar.gz |
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-rw-r--r-- | mpn/s390_64/README | 77 |
1 files changed, 77 insertions, 0 deletions
diff --git a/mpn/s390_64/README b/mpn/s390_64/README new file mode 100644 index 000000000..82b68a080 --- /dev/null +++ b/mpn/s390_64/README @@ -0,0 +1,77 @@ +Copyright 2011 Free Software Foundation, Inc. + +This file is part of the GNU MP Library. + +The GNU MP Library is free software; you can redistribute it and/or modify +it under the terms of the GNU Lesser General Public License as published by +the Free Software Foundation; either version 3 of the License, or (at your +option) any later version. + +The GNU MP Library is distributed in the hope that it will be useful, but +WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY +or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public +License for more details. + +You should have received a copy of the GNU Lesser General Public License +along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. + + + +There are 5 generations of 64-but s390 processors, z900, z990, z9, +z10, and z196. The current GMP code was optimised for the two oldest, +z900 and z990. + + +mpn_copyi + +This code makes use of a loop around MVC. It almost surely runs very +close to optimally. A small improvement could be done by using one +MVC for size 256 bytes, now we use two (we use an extra MVC when +copying any multiple of 256 bytes). + + +mpn_copyd + +We have tried several feed-in variants here, branch tree, jump table +and computed goto. The fastest (on z990) turned out to be computed +goto. + +An approach not tried is EX of LMG and STMG, modifying the register set +on-the-fly. Using that trick, we could completely avoid using +separate feed-in paths. + + +mpn_lshift, mpn_rshift + +The current code runs at pipeline decode bandwith on z990. + + +mpn_add_n, mpn_sub_n + +The current code is 4-way unrolled. It should be unrolled more, at +least 8x, in order to reach 2.5 c/l. + + +mpn_mul_1, mpn_addmul_1, mpn_submul_1 + +The current code is very naive, but due to the non-pipelined nature of +MLGR on z900 and z990, more sophisticated code would not gain much. + +On z10 one would need to cluster at least 4 MLGR together, in order to +reduce stalling. + +On z196, one surely want to use unrolling and pipelining, to perhaps +reach around 12 c/l. A major issue here and on z10 is ALCGR's 3 cycle +stalling. + + +mpn_mul_2, mpn_addmul_2 + +At least for older machines (z900, z990) with very slow MLGR, we +should use Karatsuba's algorithm on 2-limb units, making mul_2 and +addmul_2 the main multiplicaton primitives. The newer machines might +benefit less from this approach, perhaps in particular z10, where MLGR +clustering is more important. + +With Karatsuba, one could hope for around 16 cycles per accumulated +128 cross product, on z990. |