Re: [PATCH v2 2/2] sched_ext: Add cpuperf support

[Tejun Heo <tj@kernel.org>]

Hello,

On Fri, Jul 12, 2024 at 12:12:32PM +0200, Vincent Guittot wrote:
...
> II failed to setup my dev system for reproducing your use case in time
> and I'm going to be away for the coming weeks so I suppose that you
> should move forward and I will look at that when back to my dev system

Thankfully, this should be pretty easy to fix up however we want afterwards.

> It seems that "make -C tools/sched_ext ARCH=arm64 LLVM=-16" doesn't
> use clang-16 everywhere like the rest of the kernel which triggers
> error on my system:

Hmm... there is llvm prefix/suffix handling in the Makefile. I wonder what's
broken.

> make -C <path-to-linux>/linux/tools/sched_ext ARCH=arm64
> LOCALVERSION=+ LLVM=-16
> O=<path-to-linux>/out/kernel/arm64-llvm/tools/sched_ext
> ...
> clang-16 -g -O0 -fPIC -std=gnu89 -Wbad-function-cast
> -Wdeclaration-after-statement -Wformat-security -Wformat-y2k
> -Winit-self -Wmissing-declarations -Wmissing-prototypes
> -Wnested-externs -Wno-system-headers -Wold-style-definition -Wpacked
> -Wredundant-decls -Wstrict-prototypes -Wswitch-default -Wswitch-enum
> -Wundef -Wwrite-strings -Wformat -Wno-type-limits -Wshadow
> -Wno-switch-enum -Werror -Wall
> -I<path-to-linux>/out/kernel/arm64-llvm/tools/sched_ext/build/obj/libbpf/
> -I<path-to-linux>/linux/tools/include
> -I<path-to-linux>/linux/tools/include/uapi -fvisibility=hidden
> -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  \
> --shared -Wl,-soname,libbpf.so.1 \
> -Wl,--version-script=libbpf.map
> <path-to-linux>/out/kernel/arm64-llvm/tools/sched_ext/build/obj/libbpf/sharedobjs/libbpf-in.o
> -lelf -lz -o <path-to-linux>/out/kernel/arm64-llvm/tools/sched_ext/build/obj/libbpf/libbpf.so.1.5.0

So, thi sis regular arm target buliding.

> clang -g -D__TARGET_ARCH_arm64 -mlittle-endian
> -I<path-to-linux>/linux/tools/sched_ext/include
> -I<path-to-linux>/linux/tools/sched_ext/include/bpf-compat
> -I<path-to-linux>/out/kernel/arm64-llvm/tools/sched_ext/build/include
> -I<path-to-linux>/linux/tools/include/uapi -I../../include -idirafter
> /usr/lib/llvm-14/lib/clang/14.0.0/include -idirafter
> /usr/local/include -idirafter /usr/include/x86_64-linux-gnu -idirafter
> /usr/include  -Wall -Wno-compare-distinct-pointer-types -O2 -mcpu=v3
> -target bpf -c scx_simple.bpf.c -o
> <path-to-linux>/out/kernel/arm64-llvm/tools/sched_ext/build/obj/sched_ext/scx_simple.bpf.o
> In file included from scx_simple.bpf.c:23:
> <path-to-linux>/linux/tools/sched_ext/include/scx/common.bpf.h:27:17:
> error: use of undeclared identifier 'SCX_DSQ_FLAG_BUILTIN'
>         _Static_assert(SCX_DSQ_FLAG_BUILTIN,
>                        ^
> fatal error: too many errors emitted, stopping now [-ferror-limit=]
> 5 warnings and 20 errors generated.

This is BPF.

The Makefile is mostly copied from other existing BPF Makefiles under tools,
so I don't quite understand why things are set up this way but

  CC := $(LLVM_PREFIX)clang$(LLVM_SUFFIX) $(CLANG_FLAGS) -fintegrated-as

is what's used to build regular targets, while

  $(CLANG) $(BPF_CFLAGS) -target bpf -c $< -o $@

is what's used to build BPF targets. It's not too out there to use a
different compiler for BPF targtes, so maybe that's why? I'll ask BPF folks.

Thanks.

-- 
tejun