[RFC PATCH v4 0/5] Improve the performance of RISC-V vector unit-stride/whole register ld/st instructions

[Max Chou]

Hi,

Sorry for the quick update the version, this version fixes the
cross-page probe checking bug that I forgot to apply to the v3 version.

This RFC patch set tries to fix the issue of
https://gitlab.com/qemu-project/qemu/-/issues/2137.

In this RFC, we added patches that
1. Provide a fast path to direct access the host ram for some vector
   load/store instructions (e.g. unmasked vector unit-stride load/store
   instructions) and perform virtual address resolution once for the
   entire vector at beginning of helper function. (Thanks for Richard
   Henderson's suggestion)
2. Replace the group elements load/store TCG ops by the group element
   load/store flow in helper functions with some assumption (e.g. no
   masking, continuous memory load/store, the endian of host and guest
   architecture are the same). (Thanks for Richard Henderson's
   suggestion)
3. Try inline the vector load/store related functions that corresponding
   most of the execution time.

This version can improve the performance of the test case provided in
https://gitlab.com/qemu-project/qemu/-/issues/2137#note_1757501369
- QEMU user mode (vlen=512): from ~51.8 sec. to ~4.5 sec.
- QEMU system mode (vlen=512): from ~125.6 sec to ~6.6 sec.

This RFC is tested with SPEC CPU2006 with test input.
We will try to measure the performance on SPEC CPU2006 benchmarks.

Series based on riscv-to-apply.next branch (commit d82f37f).

Changes from v3:
- patch 2
    - Modify vext_cont_ldst_pages for corss-page checking
- patch 3
    - Modify vext_ldst_whole for vext_cont_ldst_pages

Previous version:
- v1: https://lore.kernel.org/all/20240215192823.729209-1-max.chou@sifive.com/
- v2: https://lore.kernel.org/all/20240531174504.281461-1-max.chou@sifive.com/
- v3: 20240613141906.1276105-1-max.chou@sifive.com/">https://lore.kernel.org/all/20240613141906.1276105-1-max.chou@sifive.com/

Max Chou (5):
  accel/tcg: Avoid unnecessary call overhead from
    qemu_plugin_vcpu_mem_cb
  target/riscv: rvv: Provide a fast path using direct access to host ram
    for unmasked unit-stride load/store
  target/riscv: rvv: Provide a fast path using direct access to host ram
    for unit-stride whole register load/store
  target/riscv: rvv: Provide group continuous ld/st flow for unit-stride
    ld/st instructions
  target/riscv: Inline unit-stride ld/st and corresponding functions for
    performance

 accel/tcg/ldst_common.c.inc             |   8 +-
 target/riscv/insn_trans/trans_rvv.c.inc |   3 +
 target/riscv/vector_helper.c            | 854 +++++++++++++++++++-----
 target/riscv/vector_internals.h         |  48 ++
 4 files changed, 745 insertions(+), 168 deletions(-)

-- 
2.34.1