[RFC PATCH 0/6] Improve the performance of RISC-V vector unit-stride ld/st instructions

[Max Chou]

Hi all,

When glibc with RVV support [1], the memcpy benchmark will run 2x to 60x
slower than the scalar equivalent on QEMU and it hurts developer
productivity.

>From the performance analysis result, we can observe that the glibc
memcpy spends most of the time in the vector unit-stride load/store
helper functions.

Samples: 465K of event 'cycles:u', Event count (approx.): 1707645730664
  Children      Self  Command       Shared Object            Symbol
+   28.46%    27.85%  qemu-riscv64  qemu-riscv64             [.] vext_ldst_us
+   26.92%     0.00%  qemu-riscv64  [unknown]                [.] 
0x00000000000000ff
+   14.41%    14.41%  qemu-riscv64  qemu-riscv64             [.] 
qemu_plugin_vcpu_mem_cb
+   13.85%    13.85%  qemu-riscv64  qemu-riscv64             [.] lde_b
+   13.64%    13.64%  qemu-riscv64  qemu-riscv64             [.] cpu_stb_mmu
+    9.25%     9.19%  qemu-riscv64  qemu-riscv64             [.] cpu_ldb_mmu
+    7.81%     7.81%  qemu-riscv64  qemu-riscv64             [.] cpu_mmu_lookup
+    7.70%     7.70%  qemu-riscv64  qemu-riscv64             [.] ste_b
+    5.53%     0.00%  qemu-riscv64  qemu-riscv64             [.] adjust_addr 
(inlined)   


So this patchset tries to improve the performance of the RVV version of
glibc memcpy on QEMU by improving the corresponding helper function
quality.

The overall performance improvement can achieve following numbers
(depending on the size).
Average: 2.86X / Smallest: 1.15X / Largest: 4.49X

PS: This RFC patchset only focuses on the vle8.v & vse8.v instructions,
the next version or next serious will complete other vector ld/st part.

Regards,
Max.

[1] 
https://inbox.sourceware.org/libc-alpha/20230504074851.38763-1-hau.hsu@sifive.com

Max Chou (6):
  target/riscv: Seperate vector segment ld/st instructions
  accel/tcg: Avoid uncessary call overhead from qemu_plugin_vcpu_mem_cb
  target/riscv: Inline vext_ldst_us and coressponding function for
    performance
  accel/tcg: Inline cpu_mmu_lookup function
  accel/tcg: Inline do_ld1_mmu function
  accel/tcg: Inline do_st1_mmu function

 accel/tcg/ldst_common.c.inc             |  40 ++++++--
 accel/tcg/user-exec.c                   |  17 ++--
 target/riscv/helper.h                   |   4 +
 target/riscv/insn32.decode              |  11 +-
 target/riscv/insn_trans/trans_rvv.c.inc |  61 +++++++++++
 target/riscv/vector_helper.c            | 130 +++++++++++++++++++-----
 6 files changed, 221 insertions(+), 42 deletions(-)

-- 
2.34.1