On Mon, 13 Jul 2020 at 20:37, Luke Nelson <lukenels@xxxxxxxxxxxxxxxxx> wrote: > > This patch series enables using compressed riscv (RVC) instructions > in the rv64 BPF JIT. > First of all; Really nice work. I like this, and it makes the code easier to read as well (e.g. emit_mv). I'm a bit curious why you only did it for RV64, and not RV32? I have some minor comments on the patches. I strongly encourage you to submit this as a proper (non-RFC) set for bpf-next. Cheers, Björn > RVC is a standard riscv extension that adds a set of compressed, > 2-byte instructions that can replace some regular 4-byte instructions > for improved code density. > > This series first modifies the JIT to support using 2-byte instructions > (e.g., in jump offset computations), then adds RVC encoding and > helper functions, and finally uses the helper functions to optimize > the rv64 JIT. > > I used our formal verification framework, Serval, to verify the > correctness of the RVC encodings and their uses in the rv64 JIT. > > The JIT continues to pass all tests in lib/test_bpf.c, and introduces > no new failures to test_verifier; both with and without RVC being enabled. > > The following are examples of the JITed code for the verifier selftest > "direct packet read test#3 for CGROUP_SKB OK", without and with RVC > enabled, respectively. The former uses 178 bytes, and the latter uses 112, > for a ~37% reduction in code size for this example. > > Without RVC: > > 0: 02000813 addi a6,zero,32 > 4: fd010113 addi sp,sp,-48 > 8: 02813423 sd s0,40(sp) > c: 02913023 sd s1,32(sp) > 10: 01213c23 sd s2,24(sp) > 14: 01313823 sd s3,16(sp) > 18: 01413423 sd s4,8(sp) > 1c: 03010413 addi s0,sp,48 > 20: 03056683 lwu a3,48(a0) > 24: 02069693 slli a3,a3,0x20 > 28: 0206d693 srli a3,a3,0x20 > 2c: 03456703 lwu a4,52(a0) > 30: 02071713 slli a4,a4,0x20 > 34: 02075713 srli a4,a4,0x20 > 38: 03856483 lwu s1,56(a0) > 3c: 02049493 slli s1,s1,0x20 > 40: 0204d493 srli s1,s1,0x20 > 44: 03c56903 lwu s2,60(a0) > 48: 02091913 slli s2,s2,0x20 > 4c: 02095913 srli s2,s2,0x20 > 50: 04056983 lwu s3,64(a0) > 54: 02099993 slli s3,s3,0x20 > 58: 0209d993 srli s3,s3,0x20 > 5c: 09056a03 lwu s4,144(a0) > 60: 020a1a13 slli s4,s4,0x20 > 64: 020a5a13 srli s4,s4,0x20 > 68: 00900313 addi t1,zero,9 > 6c: 006a7463 bgeu s4,t1,0x74 > 70: 00000a13 addi s4,zero,0 > 74: 02d52823 sw a3,48(a0) > 78: 02e52a23 sw a4,52(a0) > 7c: 02952c23 sw s1,56(a0) > 80: 03252e23 sw s2,60(a0) > 84: 05352023 sw s3,64(a0) > 88: 00000793 addi a5,zero,0 > 8c: 02813403 ld s0,40(sp) > 90: 02013483 ld s1,32(sp) > 94: 01813903 ld s2,24(sp) > 98: 01013983 ld s3,16(sp) > 9c: 00813a03 ld s4,8(sp) > a0: 03010113 addi sp,sp,48 > a4: 00078513 addi a0,a5,0 > a8: 00008067 jalr zero,0(ra) > > With RVC: > > 0: 02000813 addi a6,zero,32 > 4: 7179 c.addi16sp sp,-48 > 6: f422 c.sdsp s0,40(sp) > 8: f026 c.sdsp s1,32(sp) > a: ec4a c.sdsp s2,24(sp) > c: e84e c.sdsp s3,16(sp) > e: e452 c.sdsp s4,8(sp) > 10: 1800 c.addi4spn s0,sp,48 > 12: 03056683 lwu a3,48(a0) > 16: 1682 c.slli a3,0x20 > 18: 9281 c.srli a3,0x20 > 1a: 03456703 lwu a4,52(a0) > 1e: 1702 c.slli a4,0x20 > 20: 9301 c.srli a4,0x20 > 22: 03856483 lwu s1,56(a0) > 26: 1482 c.slli s1,0x20 > 28: 9081 c.srli s1,0x20 > 2a: 03c56903 lwu s2,60(a0) > 2e: 1902 c.slli s2,0x20 > 30: 02095913 srli s2,s2,0x20 > 34: 04056983 lwu s3,64(a0) > 38: 1982 c.slli s3,0x20 > 3a: 0209d993 srli s3,s3,0x20 > 3e: 09056a03 lwu s4,144(a0) > 42: 1a02 c.slli s4,0x20 > 44: 020a5a13 srli s4,s4,0x20 > 48: 4325 c.li t1,9 > 4a: 006a7363 bgeu s4,t1,0x50 > 4e: 4a01 c.li s4,0 > 50: d914 c.sw a3,48(a0) > 52: d958 c.sw a4,52(a0) > 54: dd04 c.sw s1,56(a0) > 56: 03252e23 sw s2,60(a0) > 5a: 05352023 sw s3,64(a0) > 5e: 4781 c.li a5,0 > 60: 7422 c.ldsp s0,40(sp) > 62: 7482 c.ldsp s1,32(sp) > 64: 6962 c.ldsp s2,24(sp) > 66: 69c2 c.ldsp s3,16(sp) > 68: 6a22 c.ldsp s4,8(sp) > 6a: 6145 c.addi16sp sp,48 > 6c: 853e c.mv a0,a5 > 6e: 8082 c.jr ra > > Luke Nelson (3): > bpf, riscv: Modify JIT ctx to support compressed instructions > bpf, riscv: Add encodings for compressed instructions > bpf, riscv: Use compressed instructions in the rv64 JIT > > arch/riscv/net/bpf_jit.h | 495 +++++++++++++++++++++++++++++++- > arch/riscv/net/bpf_jit_comp32.c | 14 +- > arch/riscv/net/bpf_jit_comp64.c | 287 +++++++++--------- > arch/riscv/net/bpf_jit_core.c | 6 +- > 4 files changed, 650 insertions(+), 152 deletions(-) > > -- > 2.25.1 >
