`ERROR: perf_event_open error : unknown architecture` on riscv64

[giordano]

I guess that's because of

LinuxPerf.jl/src/LinuxPerf.jl

Lines 160 to 172 in e7dfcbd

	const SYS_perf_event_open = if Sys.ARCH === :x86_64
	Clong(298)
	elseif Sys.ARCH === :i686
	Clong(336)
	elseif Sys.ARCH === :aarch64
	Clong(241)
	elseif Sys.ARCH === :arm
	Clong(364)
	elseif Sys.ARCH === :powerpc64le || Sys.ARCH === :ppc64le
	Clong(319)
	else
	Clong(-1) # sentinel for unknown syscall ID
	end

Where are those magic numbers coming from?

[Zentrik]

https://jborza.com/post/2021-05-11-riscv-linux-syscalls/ says SYS_perf_event_open is 241 (search perf_event_open) and for SYS_prctl its 167.

[giordano]

Thanks, I got to that table a few minutes after opening the ticket! However with

diff --git a/src/LinuxPerf.jl b/src/LinuxPerf.jl
index 7326cb3..fd6c17c 100644
--- a/src/LinuxPerf.jl
+++ b/src/LinuxPerf.jl
@@ -167,6 +167,9 @@ elseif Sys.ARCH === :arm
     Clong(364)
 elseif Sys.ARCH === :powerpc64le || Sys.ARCH === :ppc64le
     Clong(319)
+elseif Sys.ARCH === :riscv64 || Sys.ARCH === :rv64
+    # See syscalls table at https://jborza.com/post/2021-05-11-riscv-linux-syscalls/
+    Clong(241)
 else
     Clong(-1) # sentinel for unknown syscall ID
 end
@@ -350,6 +353,9 @@ elseif Sys.ARCH === :arm
     Clong(172)
 elseif Sys.ARCH === :powerpc64le || Sys.ARCH === :ppc64le
     Clong(171)
+elseif Sys.ARCH === :riscv64 || Sys.ARCH === :rv64
+    # See syscalls table at https://jborza.com/post/2021-05-11-riscv-linux-syscalls/
+    Clong(167)
 else
     Clong(-1) # sentinel for unknown syscall ID
 end

I get

julia> @pstats 1 + 1
ERROR: perf_event_open error : Function not implemented
Stacktrace:
 [1] error(s::String)
   @ Base ./error.jl:44
 [2] LinuxPerf.EventGroup(types::Vector{LinuxPerf.EventTypeExt}; warn_unsupported::Bool, userspace_only::Bool, pinned::Bool, exclusive::Bool, pid::Int32)
   @ LinuxPerf ~/.julia/dev/LinuxPerf/src/LinuxPerf.jl:317

This may be due to the kernel I'm using on this machine? It's

$ uname -a
Linux rvc23 5.15.0-starfive #1 SMP Mon Dec 19 07:56:37 EST 2022 riscv64 GNU/Linux

It's a bit old, I have access to another board with a much newer kernel v6.6.36, but I can't use LinuxPerf there because of JuliaLang/julia#57019 (Crayons is an indirect dependency of this package).

[giordano]

Yeah, it's probably a kernel issue, on a different machine it works:

julia> @pstats 1 + 1
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
┌ cpu-cycles               3.23e+05  100.0%  #  1.7 cycles per ns
│ stalled-cycles-frontend  0.00e+00  100.0%  #  0.0% of cycles
└ stalled-cycles-backend   0.00e+00  100.0%  #  0.0% of cycles
┌ instructions             4.54e+04  100.0%  #  0.1 insns per cycle
│ branch-instructions      0.00e+00  100.0%  #  0.0% of insns
└ branch-misses            0.00e+00  100.0%  #  NaN% of branch insns
┌ task-clock               9.39e+04  100.0%  # 93.9 μs
│ context-switches         0.00e+00  100.0%
│ cpu-migrations           0.00e+00  100.0%
└ page-faults              0.00e+00  100.0%
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

shell> uname -a
Linux rvc24 6.1.22 #2 SMP Thu May  4 19:24:40 CST 2023 riscv64 GNU/Linux

🥳