Re: Building perf with BUILD_BPF_SKEL=1 by default

Song Liu
2021-12-03T20:06:05Z

> On Dec 3, 2021, at 5:28 AM, Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
>
> Em Fri, Dec 03, 2021 at 10:10:42AM -0300, Arnaldo Carvalho de Melo escreveu:
>> Hi Song,
>>
>> So I'm changing all my containers to build with BUILD_BPF_SKEL=1
>> to then make this the default, so far older containers fail either
>> because the clang available is too old, so I've added a NO_BUILD_BPF_SKEL=1
>> env var to disable that in those containers and then there is this other
>> case where clang is recent enough but:
>>
>> util/bpf_skel/bperf_leader.bpf.c:13:20: error: use of undeclared identifier 'BPF_F_PRESERVE_ELEMS'
>> __uint(map_flags, BPF_F_PRESERVE_ELEMS);
>>
>> Because the system's /usr/include/linux/bpf.h doesn't have that
>> BPF_F_PRESERVE_ELEMS enum entry.
>>
>> These are enums to make them available via BTF, but then I can't use
>> the:
>>
>> #ifdef BPF_F_PRESERVE_ELEMS
>> #define BPF_F_PRESERVE_ELEMS (1U << 11)
>> #endif
>>
>> approach.
>>
>> But then we _have_ it in the tools/include/uapi/linux/bpf.h we ship:
>>
>> $ grep BPF_F_PRESERVE_ELEMS tools/include/uapi/linux/bpf.h
>> BPF_F_PRESERVE_ELEMS = (1U << 11),
>> $
>>
>> so we need to switch to using it somehow, this way we can build in more
>> systems and make bperf and other BPF enabled features.
>>
>> From a quick look I couldn't find where to add
>> $(sourcedir)/tools/include/uapi/ to the include path used to build
>> util/bpf_skel/bperf_leader.bpf.c, should be easy, can you take a look?
>
> The failure for fedora:32, which seems to be on the threshold for clang
> to be considered recent enough for building skels fails differently:
>
> clang version 10.0.1 (Fedora 10.0.1-3.fc32)
> Target: x86_64-unknown-linux-gnu
> Thread model: posix
> InstalledDir: /usr/bin
> Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-redhat-linux/10
> Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/10
> Selected GCC installation: /usr/bin/../lib/gcc/x86_64-redhat-linux/10
> Candidate multilib: .;@m64
> Candidate multilib: 32;@m32
> Selected multilib: .;@m64
> + '[' '!' ']'
> + rm -rf /tmp/build/perf
> + mkdir /tmp/build/perf
> + make ARCH= CROSS_COMPILE= EXTRA_CFLAGS= BUILD_BPF_SKEL=1 -C tools/perf O=/tmp/build/perf
> make: Entering directory '/git/perf-5.16.0-rc3/tools/perf'
> BUILD: Doing 'make -j32' parallel build
> HOSTCC /tmp/build/perf/fixdep.o
> HOSTLD /tmp/build/perf/fixdep-in.o
> LINK /tmp/build/perf/fixdep
> /bin/sh: -c: line 0: syntax error near unexpected token `('
> /bin/sh: -c: line 0: `expr bison (GNU Bison) 3.5 \>\= 371'
> Makefile.config:997: No libbabeltrace found, disables 'perf data' CTF format support, please install libbabeltrace-dev[el]/libbabeltrace-ctf-dev
>
> Auto-detecting system features:
> ... dwarf: [ on ]
> ... dwarf_getlocations: [ on ]
> ... glibc: [ on ]
> ... libbfd: [ on ]
> ... libbfd-buildid: [ on ]
> ... libcap: [ on ]
> ... libelf: [ on ]
> ... libnuma: [ on ]
> ... numa_num_possible_cpus: [ on ]
> ... libperl: [ on ]
> ... libpython: [ on ]
> ... libcrypto: [ on ]
> ... libunwind: [ on ]
> ... libdw-dwarf-unwind: [ on ]
> ... zlib: [ on ]
> ... lzma: [ on ]
> ... get_cpuid: [ on ]
> ... bpf: [ on ]
> ... libaio: [ on ]
> ... libzstd: [ on ]
> ... disassembler-four-args: [ on ]
>
>
> GEN /tmp/build/perf/common-cmds.h
> PERF_VERSION = 5.16.rc3.g0c338bcdfdb1
> CC /tmp/build/perf/exec-cmd.o
> CC /tmp/build/perf/help.o
> CC /tmp/build/perf/cpu.o
> CC /tmp/build/perf/pager.o
> CC /tmp/build/perf/debug.o
> GEN perf-archive
> CC /tmp/build/perf/parse-options.o
> CC /tmp/build/perf/str_error_r.o
> GEN perf-with-kcore
> CC /tmp/build/perf/run-command.o
> CC /tmp/build/perf/sigchain.o
> GEN perf-iostat
> MKDIR /tmp/build/perf/fd/
> MKDIR /tmp/build/perf/fs/
> CC /tmp/build/perf/subcmd-config.o
> MKDIR /tmp/build/perf/jvmti/
> MKDIR /tmp/build/perf/fs/
> MKDIR /tmp/build/perf/jvmti/
> CC /tmp/build/perf/dlfilters/dlfilter-test-api-v0.o
> CC /tmp/build/perf/dlfilters/dlfilter-show-cycles.o
> MKDIR /tmp/build/perf/jvmti/
> CC /tmp/build/perf/fd/array.o
> MKDIR /tmp/build/perf/fs/
> CC /tmp/build/perf/fs/fs.o
> MKDIR /tmp/build/perf/jvmti/
> MKDIR /tmp/build/perf/pmu-events/
> CC /tmp/build/perf/event-parse.o
> MKDIR /tmp/build/perf/pmu-events/
> CC /tmp/build/perf/jvmti/libjvmti.o
> CC /tmp/build/perf/jvmti/jvmti_agent.o
> CC /tmp/build/perf/fs/tracing_path.o
> CC /tmp/build/perf/jvmti/libstring.o
> CC /tmp/build/perf/fs/cgroup.o
> HOSTCC /tmp/build/perf/pmu-events/json.o
> CC /tmp/build/perf/jvmti/libctype.o
> CC /tmp/build/perf/core.o
> HOSTCC /tmp/build/perf/pmu-events/jsmn.o
> MKDIR /tmp/build/perf/pmu-events/
> HOSTCC /tmp/build/perf/pmu-events/jevents.o
> CC /tmp/build/perf/cpumap.o
> CC /tmp/build/perf/plugin_jbd2.o
> CC /tmp/build/perf/plugin_hrtimer.o
> CC /tmp/build/perf/plugin_kmem.o
> CC /tmp/build/perf/threadmap.o
> CC /tmp/build/perf/plugin_kvm.o
> CC /tmp/build/perf/evsel.o
> CC /tmp/build/perf/plugin_mac80211.o
> LINK /tmp/build/perf/dlfilters/dlfilter-show-cycles.so
> CC /tmp/build/perf/plugin_sched_switch.o
> make[3]: *** No rule to make target 'kernelversion'. Stop.
> CC /tmp/build/perf/plugin_function.o
> LD /tmp/build/perf/fd/libapi-in.o
> CC /tmp/build/perf/event-plugin.o
> GEN /tmp/build/perf/libbpf/bpf_helper_defs.h
> CC /tmp/build/perf/plugin_futex.o
> CC /tmp/build/perf/plugin_xen.o
> CC /tmp/build/perf/plugin_scsi.o
> CC /tmp/build/perf/evlist.o
> INSTALL /tmp/build/perf/libbpf/include/bpf/bpf.h
> LD /tmp/build/perf/plugin_jbd2-in.o
> CC /tmp/build/perf/plugin_cfg80211.o
> INSTALL /tmp/build/perf/libbpf/include/bpf/libbpf.h
> LD /tmp/build/perf/plugin_hrtimer-in.o
> LD /tmp/build/perf/fs/libapi-in.o
> LD /tmp/build/perf/plugin_kmem-in.o
> CC /tmp/build/perf/plugin_tlb.o
> LINK /tmp/build/perf/dlfilters/dlfilter-test-api-v0.so
> CC /tmp/build/perf/mmap.o
> CC /tmp/build/perf/zalloc.o
> LINK /tmp/build/perf/plugin_jbd2.so
> LINK /tmp/build/perf/plugin_hrtimer.so
> INSTALL /tmp/build/perf/libbpf/include/bpf/btf.h
> CC /tmp/build/perf/xyarray.o
> CC /tmp/build/perf/trace-seq.o
> LD /tmp/build/perf/plugin_mac80211-in.o
> LD /tmp/build/perf/libapi-in.o
> LD /tmp/build/perf/plugin_kvm-in.o
> CC /tmp/build/perf/parse-filter.o
> CC /tmp/build/perf/parse-utils.o
> LD /tmp/build/perf/plugin_sched_switch-in.o
> CC /tmp/build/perf/kbuffer-parse.o
> CC /tmp/build/perf/tep_strerror.o
> HOSTLD /tmp/build/perf/pmu-events/jevents-in.o
> INSTALL /tmp/build/perf/libbpf/include/bpf/libbpf_common.h
> INSTALL /tmp/build/perf/libbpf/include/bpf/libbpf_legacy.h
> CC /tmp/build/perf/event-parse-api.o
> INSTALL /tmp/build/perf/libbpf/include/bpf/xsk.h
> INSTALL /tmp/build/perf/libbpf/include/bpf/bpf_helpers.h
> AR /tmp/build/perf/libapi.a
> LD /tmp/build/perf/plugin_function-in.o
> INSTALL /tmp/build/perf/libbpf/include/bpf/bpf_tracing.h
> LINK /tmp/build/perf/plugin_kmem.so
> LINK /tmp/build/perf/plugin_mac80211.so
> LINK /tmp/build/perf/plugin_kvm.so
> LD /tmp/build/perf/plugin_xen-in.o
> LINK /tmp/build/perf/plugin_sched_switch.so
> LD /tmp/build/perf/plugin_cfg80211-in.o
> CC /tmp/build/perf/lib.o
> INSTALL /tmp/build/perf/libbpf/include/bpf/bpf_endian.h
> LD /tmp/build/perf/plugin_futex-in.o
> LD /tmp/build/perf/plugin_scsi-in.o
> INSTALL /tmp/build/perf/libbpf/include/bpf/bpf_core_read.h
> LINK /tmp/build/perf/pmu-events/jevents
> LD /tmp/build/perf/plugin_tlb-in.o
> LINK /tmp/build/perf/plugin_function.so
> LINK /tmp/build/perf/plugin_xen.so
> INSTALL /tmp/build/perf/libbpf/include/bpf/skel_internal.h
> LINK /tmp/build/perf/plugin_cfg80211.so
> INSTALL /tmp/build/perf/libbpf/include/bpf/libbpf_version.h
> LINK /tmp/build/perf/plugin_futex.so
> INSTALL /tmp/build/perf/libbpf/include/bpf/bpf_helper_defs.h
> LINK /tmp/build/perf/plugin_scsi.so
> LD /tmp/build/perf/jvmti/jvmti-in.o
> LINK /tmp/build/perf/plugin_tlb.so
> MKDIR /tmp/build/perf/libbpf/staticobjs/
> MKDIR /tmp/build/perf/libbpf/staticobjs/
> MKDIR /tmp/build/perf/libbpf/staticobjs/
> MKDIR /tmp/build/perf/libbpf/staticobjs/
> MKDIR /tmp/build/perf/libbpf/staticobjs/
> LD /tmp/build/perf/libsubcmd-in.o
> MKDIR /tmp/build/perf/libbpf/staticobjs/
> MKDIR /tmp/build/perf/libbpf/staticobjs/
> MKDIR /tmp/build/perf/libbpf/staticobjs/
> MKDIR /tmp/build/perf/libbpf/staticobjs/
> CC /tmp/build/perf/libbpf/staticobjs/xsk.o
> CC /tmp/build/perf/libbpf/staticobjs/libbpf.o
> LINK /tmp/build/perf/libperf-jvmti.so
> CC /tmp/build/perf/libbpf/staticobjs/bpf.o
> CC /tmp/build/perf/libbpf/staticobjs/nlattr.o
> CC /tmp/build/perf/libbpf/staticobjs/btf.o
> CC /tmp/build/perf/libbpf/staticobjs/libbpf_errno.o
> CC /tmp/build/perf/libbpf/staticobjs/hashmap.o
> CC /tmp/build/perf/libbpf/staticobjs/str_error.o
> CC /tmp/build/perf/libbpf/staticobjs/netlink.o
> CC /tmp/build/perf/libbpf/staticobjs/btf_dump.o
> CC /tmp/build/perf/libbpf/staticobjs/bpf_prog_linfo.o
> CC /tmp/build/perf/libbpf/staticobjs/libbpf_probes.o
> CC /tmp/build/perf/libbpf/staticobjs/ringbuf.o
> CC /tmp/build/perf/libbpf/staticobjs/strset.o
> GEN /tmp/build/perf/libtraceevent-dynamic-list
> CC /tmp/build/perf/libbpf/staticobjs/linker.o
> CC /tmp/build/perf/libbpf/staticobjs/gen_loader.o
> CC /tmp/build/perf/libbpf/staticobjs/relo_core.o
> AR /tmp/build/perf/libsubcmd.a
> LD /tmp/build/perf/libtraceevent-in.o
> GEN /tmp/build/perf/pmu-events/pmu-events.c
> LINK /tmp/build/perf/libtraceevent.a
> LD /tmp/build/perf/libperf-in.o
> AR /tmp/build/perf/libperf.a
> GEN /tmp/build/perf/python/perf.so
> CC /tmp/build/perf/pmu-events/pmu-events.o
>
> Auto-detecting system features:
> ... libbfd: [ on ]
> ... disassembler-four-args: [ on ]
> ... zlib: [ on ]
> ... libcap: [ on ]
> ... clang-bpf-co-re: [ on ]
>
>
> MKDIR /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf//include/bpf
> MKDIR /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/
> MKDIR /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/
> INSTALL /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf//include/bpf/hashmap.h
> GEN /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/bpf_helper_defs.h
> INSTALL /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf//include/bpf/bpf.h
> INSTALL /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf//include/bpf/libbpf.h
> INSTALL /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf//include/bpf/btf.h
> INSTALL /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf//include/bpf/libbpf_common.h
> INSTALL /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf//include/bpf/libbpf_legacy.h
> INSTALL /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf//include/bpf/xsk.h
> INSTALL /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf//include/bpf/bpf_helpers.h
> INSTALL /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf//include/bpf/bpf_tracing.h
> INSTALL /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf//include/bpf/bpf_endian.h
> INSTALL /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf//include/bpf/bpf_core_read.h
> INSTALL /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf//include/bpf/skel_internal.h
> INSTALL /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf//include/bpf/libbpf_version.h
> INSTALL /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf//include/bpf/bpf_helper_defs.h
> MKDIR /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/
> MKDIR /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/
> MKDIR /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/
> MKDIR /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/
> MKDIR /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/
> MKDIR /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/
> MKDIR /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/
> MKDIR /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/
> MKDIR /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/
> MKDIR /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/
> MKDIR /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/btf_dump.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/libbpf.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/bpf.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/nlattr.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/btf.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/ringbuf.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/libbpf_errno.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/str_error.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/netlink.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/bpf_prog_linfo.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/strset.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/libbpf_probes.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/xsk.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/hashmap.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/linker.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/gen_loader.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/relo_core.o
> LD /tmp/build/perf/pmu-events/pmu-events-in.o
> LD /tmp/build/perf/libbpf/staticobjs/libbpf-in.o
> LINK /tmp/build/perf/libbpf/libbpf.a
> LD /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/staticobjs/libbpf-in.o
> LINK /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/libbpf/libbpf.a
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/common.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/main.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/json_writer.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/gen.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/xlated_dumper.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/btf.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/btf_dumper.o
> CC /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/disasm.o
> LINK /tmp/build/perf/util/bpf_skel/.tmp//bootstrap/bpftool
> GEN /tmp/build/perf/util/bpf_skel/vmlinux.h
> CLANG /tmp/build/perf/util/bpf_skel/.tmp/bpf_prog_profiler.bpf.o
> CLANG /tmp/build/perf/util/bpf_skel/.tmp/bperf_leader.bpf.o
> CLANG /tmp/build/perf/util/bpf_skel/.tmp/bperf_follower.bpf.o
> CLANG /tmp/build/perf/util/bpf_skel/.tmp/bperf_cgroup.bpf.o
> GENSKEL /tmp/build/perf/util/bpf_skel/bpf_prog_profiler.skel.h
> GENSKEL /tmp/build/perf/util/bpf_skel/bperf_leader.skel.h
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(7) .eh_frame
> libbpf: elf: skipping relo section(12) .rel.eh_frame for section(7) .eh_frame
> libbpf: map 'prev_readings': unexpected def kind var.
> Error: failed to open BPF object file: Invalid argument
> make[2]: *** [Makefile.perf:1076: /tmp/build/perf/util/bpf_skel/bperf_leader.skel.h] Error 255
> make[2]: *** Waiting for unfinished jobs....
> make[1]: *** [Makefile.perf:240: sub-make] Error 2
> make: *** [Makefile:70: all] Error 2
> make: Leaving directory '/git/perf-5.16.0-rc3/tools/perf'
> + exit 1
> [perfbuilder@five 32]$

Cc Andrii.

Could you please try the fix below?

If it doesn't work, could you please dump btf for debugging?

bpftool btf dump file /tmp/build/perf/util/bpf_skel/.tmp/bperf_leader.bpf.o

Thanks,
Song

diff --git i/tools/perf/util/bpf_skel/bperf_follower.bpf.c w/tools/perf/util/bpf_skel/bperf_follower.bpf.c
index 4a6acfde14937..bd191c9bc49bc 100644
--- i/tools/perf/util/bpf_skel/bperf_follower.bpf.c
+++ w/tools/perf/util/bpf_skel/bperf_follower.bpf.c
@@ -6,8 +6,19 @@
#include "bperf.h"
#include "bperf_u.h"

-reading_map diff_readings SEC(".maps");
-reading_map accum_readings SEC(".maps");
+struct {
+ __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
+ __uint(key_size, sizeof(__u32));
+ __uint(value_size, sizeof(struct bpf_perf_event_value));
+ __uint(max_entries, 1);
+} diff_readings SEC(".maps");
+
+struct {
+ __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
+ __uint(key_size, sizeof(__u32));
+ __uint(value_size, sizeof(struct bpf_perf_event_value));
+ __uint(max_entries, 1);
+} accum_readings SEC(".maps");

struct {
__uint(type, BPF_MAP_TYPE_HASH);
diff --git i/tools/perf/util/bpf_skel/bperf_leader.bpf.c w/tools/perf/util/bpf_skel/bperf_leader.bpf.c
index 40d962b058634..d52a335e63f0f 100644
--- i/tools/perf/util/bpf_skel/bperf_leader.bpf.c
+++ w/tools/perf/util/bpf_skel/bperf_leader.bpf.c
@@ -12,8 +12,19 @@ struct {
__uint(map_flags, BPF_F_PRESERVE_ELEMS);
} events SEC(".maps");

-reading_map prev_readings SEC(".maps");
-reading_map diff_readings SEC(".maps");
+struct {
+ __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
+ __uint(key_size, sizeof(__u32));
+ __uint(value_size, sizeof(struct bpf_perf_event_value));
+ __uint(max_entries, 1);
+} prev_readings SEC(".maps");
+
+struct {
+ __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
+ __uint(key_size, sizeof(__u32));
+ __uint(value_size, sizeof(struct bpf_perf_event_value));
+ __uint(max_entries, 1);
+} diff_readings SEC(".maps");

SEC("raw_tp/sched_switch")
int BPF_PROG(on_switch)