| Message ID | 20240215192823.729209-1-max.chou@sifive.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Improve the performance of RISC-V vector unit-stride ld/st instructions | expand |
On 2/15/24 09:28, Max Chou wrote: > 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. You are still not tackling the root problem, which is over-use of the full out-of-line load/store routines. The reason that cpu_mmu_lookup is in that list is because you are performing the full virtual address resolution for each and every byte. The only way to make a real improvement is to perform virtual address resolution *once* for the entire vector. I refer to my previous advice: https://gitlab.com/qemu-project/qemu/-/issues/2137#note_1757501369 r~
Hi Richard, Thank you for the suggestion and the reference. I'm trying to follow the reference to implement it and I'll send another version for this. Thanks a lot, Max On 2024/2/16 4:24 AM, Richard Henderson wrote: > On 2/15/24 09:28, Max Chou wrote: >> 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. > > You are still not tackling the root problem, which is over-use of the > full out-of-line load/store routines. The reason that cpu_mmu_lookup > is in that list is because you are performing the full virtual address > resolution for each and every byte. > > The only way to make a real improvement is to perform virtual address > resolution *once* for the entire vector. I refer to my previous advice: > > https://gitlab.com/qemu-project/qemu/-/issues/2137#note_1757501369 > > > r~
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(-)