perf test record.sh: Raise limit of open file descriptors

Subtest for system-wide record with '--threads=cpu' option fails due
to a limit of open file descriptors on systems with 128 or more CPUs
as the default limit is set to 1024.

The number of open file descriptors should be slightly above
nmb_events*nmb_cpus + nmb_cpus(for perf.data.n) + 4*nmb_cpus(for pipes),
which equals 8*nmb_cpus. Therefore, temporarily raise the limit to
16*nmb_cpus for the test.

Committer notes:

Instead of disabling ShellCheck warnings all the uses of 'uname -n',
i.e. those:

  In tests/shell/record.sh line 35:
  default_fd_limit=$(ulimit -Sn)
                            ^-^ SC3045 (warning): In POSIX sh, ulimit -S is undefined.

We can just switch from using '/bin/sh' to '/bin/bash' for this test, as
bash _has_ 'ulimit -n', so ShellCheck will not emit that warning.

There are dozens of 'perf test' shell tests that do just that,
'/bin/bash' is a reasonable expectation for those tests.
Signed-off-by: Veronika Molnarova <vmolnaro@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Radostin Stoyanov <rstoyano@redhat.com>
Link: https://lore.kernel.org/linux-perf-users/20240429085721.10122-1-vmolnaro@redhat.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/shell/record.sh

-#!/bin/sh
+#!/bin/bash
 # perf record tests
 # SPDX-License-Identifier: GPL-2.0
 
@@ -23,6 +23,15 @@ br_cntr_file="/caps/branch_counter_nr"
 br_cntr_output="branch stack counters"
 br_cntr_script_output="br_cntr: A"
 
+default_fd_limit=$(ulimit -Sn)
+# With option --threads=cpu the number of open file descriptors should be
+# equal to sum of:    nmb_cpus * nmb_events (2+dummy),
+#                     nmb_threads for perf.data.n (equal to nmb_cpus) and
+#                     2*nmb_cpus of pipes = 4*nmb_cpus (each pipe has 2 ends)
+# All together it needs 8*nmb_cpus file descriptors plus some are also used
+# outside of testing, thus raising the limit to 16*nmb_cpus
+min_fd_limit=$(($(getconf _NPROCESSORS_ONLN) * 16))
+
 cleanup() {
   rm -rf "${perfdata}"
   rm -rf "${perfdata}".old
@@ -197,11 +206,19 @@ test_branch_counter() {
   echo "Branch counter test [Success]"
 }
 
+# raise the limit of file descriptors to minimum
+if [[ $default_fd_limit -lt $min_fd_limit ]]; then
+       ulimit -Sn $min_fd_limit
+fi
+
 test_per_thread
 test_register_capture
 test_system_wide
 test_workload
 test_branch_counter
 
+# restore the default value
+ulimit -Sn $default_fd_limit
+
 cleanup
 exit $err