Subject: Re: [PATCH v4 44/48] perf bpf: Rename cpu to cpu_map_idx

From: Arnaldo Carvalho de Melo <[email-masked]>
Date: Mon, 10 Jan 2022 16:26:26 -0300

Em Mon, Jan 10, 2022 at 04:10:46PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Tue, Jan 04, 2022 at 10:13:47PM -0800, Ian Rogers escreveu:
> > Synchronize the caller in evsel with the called function.
> > Shorten 3 lines of code in bperf_read by using
> > perf_cpu_map__for_each_cpu.
> > This code is frequently using variables named cpu as cpu map indices,
> > which doesn't matter as all CPUs are in the CPU map. It is strange in
> > some cases the cpumap is used at all.
> 
>   CC      /tmp/build/perf/builtin-stat.o
>   INSTALL trace_plugins
>   CC      /tmp/build/perf/util/evlist.o
>   CC      /tmp/build/perf/util/evsel.o
>   CC      /tmp/build/perf/util/header.o
>   CC      /tmp/build/perf/util/bpf_counter.o
>   CC      /tmp/build/perf/util/bpf_counter_cgroup.o
>   CC      /tmp/build/perf/util/bpf_ftrace.o
> In file included from util/cpumap.h:8,
>                  from util/bpf_counter.c:23:
> util/bpf_counter.c: In function ‘bperf__read’:
> /var/home/acme/git/perf/tools/lib/perf/include/perf/cpumap.h:27:20: error: comparison of integer expressions of different signedness: ‘__u32’ {aka ‘unsigned int’} and ‘int’ [-Werror=sign-compare]
>    27 |              (idx) < perf_cpu_map__nr(cpus);                    \
>       |                    ^
> util/bpf_counter.c:626:25: note: in expansion of macro ‘perf_cpu_map__for_each_cpu’
>   626 |                         perf_cpu_map__for_each_cpu(cpu, j, all_cpu_map) {
>       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~
> util/bpf_counter.c:611:21: error: unused variable ‘num_cpu’ [-Werror=unused-variable]
>   611 |         __u32 i, j, num_cpu;
>       |                     ^~~~~~~
> cc1: all warnings being treated as errors
> make[4]: *** [/var/home/acme/git/perf/tools/build/Makefile.build:96: /tmp/build/perf/util/bpf_counter.o] Error 1
> make[4]: *** Waiting for unfinished jobs....
> make[3]: *** [/var/home/acme/git/perf/tools/build/Makefile.build:139: util] Error 2
> make[2]: *** [Makefile.perf:665: /tmp/build/perf/perf-in.o] Error 2
> make[1]: *** [Makefile.perf:240: sub-make] Error 2
> make: *** [Makefile:113: install-bin] Error 2
> make: Leaving directory '/var/home/acme/git/perf/tools/perf'
> 
>  Performance counter stats for 'make -k BUILD_BPF_SKEL=1 CORESIGHT=1 PYTHON=python3 O=/tmp/build/perf -C tools/perf install-bin':
> 
>     15,589,752,360      cycles:u
>     28,227,862,710      instructions:u            #    1.81  insn per cycle
> 
>        1.996638375 seconds time elapsed
> 
>        3.567457000 seconds user
>        0.934840000 seconds sys
> 
> 
> ⬢[acme@toolbox perf]$ git log --oneline -1
> 0083ba4c6a931fd0 (HEAD) perf bpf: Rename cpu to cpu_map_idx
> ⬢[acme@toolbox perf]$
> 
> Trying to fix...

Would be better to have the "Shorten 3 lines of code in bperf_read by
using perf_cpu_map__for_each_cpu." in a separate patch, try to do this
next time.

Below cures the two issues.

- Arnaldo

    Committer notes:

    Found when building with BUILD_BPF_SKEL=1:

    Remove unused 'num_cpu' variable in bperf__read().

    Make 'j' an 'int' as it is used in perf_cpu_map__for_each_cpu() to compare against an 'int'

diff --git a/tools/perf/util/bpf_counter.c b/tools/perf/util/bpf_counter.c
index ae5bd87ff02033c2..80d1a3a31052fe55 100644
--- a/tools/perf/util/bpf_counter.c
+++ b/tools/perf/util/bpf_counter.c
@@ -608,7 +608,8 @@ static int bperf__read(struct evsel *evsel)
 	__u32 num_cpu_bpf = cpu__max_cpu();
 	struct bpf_perf_event_value values[num_cpu_bpf];
 	int reading_map_fd, err = 0;
-	__u32 i, j, num_cpu;
+	__u32 i;
+	int j;
 
 	bperf_sync_counters(evsel);
 	reading_map_fd = bpf_map__fd(skel->maps.accum_readings);

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