On Thu, May 2, 2024 at 6:18 PM Björn Töpel <bjorn@xxxxxxxxxx> wrote: > > Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes: > > > On Tue, Apr 30, 2024 at 10:58 AM Puranjay Mohan <puranjay@xxxxxxxxxx> wrote: > >> > >> Support an instruction for resolving absolute addresses of per-CPU > >> data from their per-CPU offsets. This instruction is internal-only and > >> users are not allowed to use them directly. They will only be used for > >> internal inlining optimizations for now between BPF verifier and BPF > >> JITs. > >> > >> RISC-V uses generic per-cpu implementation where the offsets for CPUs > >> are kept in an array called __per_cpu_offset[cpu_number]. RISCV stores > >> the address of the task_struct in TP register. The first element in > >> task_struct is struct thread_info, and we can get the cpu number by > >> reading from the TP register + offsetof(struct thread_info, cpu). > >> > >> Once we have the cpu number in a register we read the offset for that > >> cpu from address: &__per_cpu_offset + cpu_number << 3. Then we add this > >> offset to the destination register. > >> > >> To measure the improvement from this change, the benchmark in [1] was > >> used on Qemu: > >> > >> Before: > >> glob-arr-inc : 1.127 ± 0.013M/s > >> arr-inc : 1.121 ± 0.004M/s > >> hash-inc : 0.681 ± 0.052M/s > >> > >> After: > >> glob-arr-inc : 1.138 ± 0.011M/s > >> arr-inc : 1.366 ± 0.006M/s > >> hash-inc : 0.676 ± 0.001M/s > >> > >> [1] https://github.com/anakryiko/linux/commit/8dec900975ef > >> > >> Signed-off-by: Puranjay Mohan <puranjay@xxxxxxxxxx> > >> --- > >> arch/riscv/net/bpf_jit_comp64.c | 24 ++++++++++++++++++++++++ > >> 1 file changed, 24 insertions(+) > >> > >> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c > >> index 15e482f2c657..99d7006f1420 100644 > >> --- a/arch/riscv/net/bpf_jit_comp64.c > >> +++ b/arch/riscv/net/bpf_jit_comp64.c > >> @@ -12,6 +12,7 @@ > >> #include <linux/stop_machine.h> > >> #include <asm/patch.h> > >> #include <asm/cfi.h> > >> +#include <asm/percpu.h> > >> #include "bpf_jit.h" > >> > >> #define RV_FENTRY_NINSNS 2 > >> @@ -1089,6 +1090,24 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx, > >> emit_or(RV_REG_T1, rd, RV_REG_T1, ctx); > >> emit_mv(rd, RV_REG_T1, ctx); > >> break; > >> + } else if (insn_is_mov_percpu_addr(insn)) { > >> + if (rd != rs) > >> + emit_mv(rd, rs, ctx); > > No biggie, but you did not fold this check into emit_mv(). > > >> +#ifdef CONFIG_SMP > >> + /* Load current CPU number in T1 */ > >> + emit_ld(RV_REG_T1, offsetof(struct thread_info, cpu), > >> + RV_REG_TP, ctx); > >> + /* << 3 because offsets are 8 bytes */ > >> + emit_slli(RV_REG_T1, RV_REG_T1, 3, ctx); > >> + /* Load address of __per_cpu_offset array in T2 */ > >> + emit_addr(RV_REG_T2, (u64)&__per_cpu_offset, extra_pass, ctx); > >> + /* Add offset of current CPU to __per_cpu_offset */ > >> + emit_add(RV_REG_T1, RV_REG_T2, RV_REG_T1, ctx); > >> + /* Load __per_cpu_offset[cpu] in T1 */ > >> + emit_ld(RV_REG_T1, 0, RV_REG_T1, ctx); > >> + /* Add the offset to Rd */ > >> + emit_add(rd, rd, RV_REG_T1, ctx); > > > > is this the right level of code indentation? > > Looks wrong. > > When the indent is fixed, feel free to add: > > Acked-by: Björn Töpel <bjorn@xxxxxxxxxx> I fixed the indent and sent it as part of: https://lore.kernel.org/all/20240502151854.9810-1-puranjay@xxxxxxxxxx/ Also, for the emit_mv() thing, I wanted to verify if we are using that somewhere for zero-extension or something. So, I thought I would send a separate patch for it. Thanks, Puranjay
