unicorn/qemu/target-arm/helper-a64.h
Emilio G. Cota cb92eea81a
target-arm: emulate aarch64's LL/SC using cmpxchg helpers
Emulating LL/SC with cmpxchg is not correct, since it can
suffer from the ABA problem. Portable parallel code, however,
is written assuming only cmpxchg--and not LL/SC--is available.
This means that in practice emulating LL/SC with cmpxchg is
a viable alternative.

The appended emulates LL/SC pairs in aarch64 with cmpxchg helpers.
This works in both user and system mode. In usermode, it avoids
pausing all other CPUs to perform the LL/SC pair. The subsequent
performance and scalability improvement is significant, as the
plots below show. They plot the throughput of atomic_add-bench
compiled for ARM and executed on a 64-core x86 machine.

Hi-res plots: http://imgur.com/a/JVc8Y

atomic_add-bench: 1000000 ops/thread, [0,1] range

18 ++---------+----------+---------+----------+----------+----------+---++
+cmpxchg +-E--+ + + + + + |
16 ++master +-H--+ ++
|| |
14 ++ ++
| | |
12 ++| ++
| | |
10 ++++ ++
8 ++E ++
|+++ |
6 ++ | ++
| | |
4 ++ | ++
| | |
2 +H++E+--- ++
+ | +E++----+E+---+--+E+----++E+------+E+------+E++----+E+---+--+E|
0 ++H-H----H-+-----H----+---------+----------+----------+----------+---++
0 10 20 30 40 50 60
Number of threads

atomic_add-bench: 1000000 ops/thread, [0,2] range

18 ++---------+----------+---------+----------+----------+----------+---++
+cmpxchg +-E--+ + + + + + |
16 ++master +-H--+ ++
| | |
14 ++E ++
| | |
12 ++| ++
|+++ |
10 ++ | ++
8 ++ | ++
| | |
6 ++ | ++
| | |
4 ++ | ++
| +E+--- |
2 +H+ +E+-----+++ +++ +++ ---+E+-----+E+------+++
+++ + +E+---+--+E+----++E+------+E+--- ++++ +++ + +E|
0 ++H-H----H-+-----H----+---------+----------+----------+----------+---++
0 10 20 30 40 50 60
Number of threads

atomic_add-bench: 1000000 ops/thread, [0,128] range

70 ++---------+----------+---------+----------+----------+----------+---++
+cmpxchg +-E--+ + + + + + |
60 ++master +-H--+ +++ ---+E+-----+E+------+E+
| +E+------E-------+E+--- |
| --- +++ |
50 ++ +++--- ++
| -+E+ |
40 ++ +++---- ++
| E- |
| --| |
30 ++ -- +++ ++
| +E+ |
20 ++E+ ++
|E+ |
| |
10 ++ ++
+ + + + + + + |
0 +HH-H----H-+-----H----+---------+----------+----------+----------+---++
0 10 20 30 40 50 60
Number of threads

atomic_add-bench: 1000000 ops/thread, [0,1024] range

160 ++---------+---------+----------+---------+----------+----------+---++
+cmpxchg +-E--+ + + + + + |
140 ++master +-H--+ +++ +++
| -+E+-----+E+-------E|
120 ++ +++ ---- +++
| +++ ----E-- |
100 ++ --E--- +++ ++
| +++ ---- +++ |
80 ++ --E-- ++
| ---- +++ |
| -+E+ |
60 ++ ---- +++ ++
| +E+- |
40 ++ -- ++
| +E+ |
20 +EE+ ++
+++ + + + + + + |
0 +HH-H---H--+-----H---+----------+---------+----------+----------+---++
0 10 20 30 40 50 60
Number of threads

Backports commit 1dd089d0eec060dcd8478735114d98421d414805 from qemu
2018-02-28 00:21:27 -05:00

51 lines
2.8 KiB
C

/*
* AArch64 specific helper definitions
*
* Copyright (c) 2013 Alexander Graf <agraf@suse.de>
*
* This 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 2 of the License, or (at your option) any later version.
*
* This 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 this library; if not, see <http://www.gnu.org/licenses/>.
*/
DEF_HELPER_FLAGS_2(udiv64, TCG_CALL_NO_RWG_SE, i64, i64, i64)
DEF_HELPER_FLAGS_2(sdiv64, TCG_CALL_NO_RWG_SE, s64, s64, s64)
DEF_HELPER_FLAGS_1(clz64, TCG_CALL_NO_RWG_SE, i64, i64)
DEF_HELPER_FLAGS_1(cls64, TCG_CALL_NO_RWG_SE, i64, i64)
DEF_HELPER_FLAGS_1(cls32, TCG_CALL_NO_RWG_SE, i32, i32)
DEF_HELPER_FLAGS_1(clz32, TCG_CALL_NO_RWG_SE, i32, i32)
DEF_HELPER_FLAGS_1(rbit64, TCG_CALL_NO_RWG_SE, i64, i64)
DEF_HELPER_3(vfp_cmps_a64, i64, f32, f32, ptr)
DEF_HELPER_3(vfp_cmpes_a64, i64, f32, f32, ptr)
DEF_HELPER_3(vfp_cmpd_a64, i64, f64, f64, ptr)
DEF_HELPER_3(vfp_cmped_a64, i64, f64, f64, ptr)
DEF_HELPER_FLAGS_5(simd_tbl, TCG_CALL_NO_RWG_SE, i64, env, i64, i64, i32, i32)
DEF_HELPER_FLAGS_3(vfp_mulxs, TCG_CALL_NO_RWG, f32, f32, f32, ptr)
DEF_HELPER_FLAGS_3(vfp_mulxd, TCG_CALL_NO_RWG, f64, f64, f64, ptr)
DEF_HELPER_FLAGS_3(neon_ceq_f64, TCG_CALL_NO_RWG, i64, i64, i64, ptr)
DEF_HELPER_FLAGS_3(neon_cge_f64, TCG_CALL_NO_RWG, i64, i64, i64, ptr)
DEF_HELPER_FLAGS_3(neon_cgt_f64, TCG_CALL_NO_RWG, i64, i64, i64, ptr)
DEF_HELPER_FLAGS_3(recpsf_f32, TCG_CALL_NO_RWG, f32, f32, f32, ptr)
DEF_HELPER_FLAGS_3(recpsf_f64, TCG_CALL_NO_RWG, f64, f64, f64, ptr)
DEF_HELPER_FLAGS_3(rsqrtsf_f32, TCG_CALL_NO_RWG, f32, f32, f32, ptr)
DEF_HELPER_FLAGS_3(rsqrtsf_f64, TCG_CALL_NO_RWG, f64, f64, f64, ptr)
DEF_HELPER_FLAGS_1(neon_addlp_s8, TCG_CALL_NO_RWG_SE, i64, i64)
DEF_HELPER_FLAGS_1(neon_addlp_u8, TCG_CALL_NO_RWG_SE, i64, i64)
DEF_HELPER_FLAGS_1(neon_addlp_s16, TCG_CALL_NO_RWG_SE, i64, i64)
DEF_HELPER_FLAGS_1(neon_addlp_u16, TCG_CALL_NO_RWG_SE, i64, i64)
DEF_HELPER_FLAGS_2(frecpx_f64, TCG_CALL_NO_RWG, f64, f64, ptr)
DEF_HELPER_FLAGS_2(frecpx_f32, TCG_CALL_NO_RWG, f32, f32, ptr)
DEF_HELPER_FLAGS_2(fcvtx_f64_to_f32, TCG_CALL_NO_RWG, f32, f64, env)
DEF_HELPER_FLAGS_3(crc32_64, TCG_CALL_NO_RWG_SE, i64, i64, i64, i32)
DEF_HELPER_FLAGS_3(crc32c_64, TCG_CALL_NO_RWG_SE, i64, i64, i64, i32)
DEF_HELPER_FLAGS_4(paired_cmpxchg64_le, TCG_CALL_NO_WG, i64, env, i64, i64, i64)
DEF_HELPER_FLAGS_4(paired_cmpxchg64_be, TCG_CALL_NO_WG, i64, env, i64, i64, i64)