Both return errno, show the string associated then.

More work needed to capture the sched_attr arg to beautify it in turn,
probably using BPF.

Before:

     0.210 ( 0.001 ms): sched_setattr(uattr: 0x7ffc684f02b0) = -22

After the patch, for this sched_attr, all other parms are zero, so not
shown:

        struct sched_attr attr = {
                .size           = sizeof(attr),
                .sched_policy   = SCHED_DEADLINE,
                .sched_runtime  = 10 * USECS_PER_SEC,
                .sched_period   = 30 * USECS_PER_SEC,
                .sched_deadline = attr.sched_period,
        };

     0.321 ( 0.002 ms): sched_setattr(uattr: 0x7ffc44116da0) = -1 EINVAL Invalid argument

  [root@jouet c]# perf trace -e sched_setattr ./sched_deadline
  Couldn't negotiate deadline: Invalid argument
     0.229 ( 0.003 ms): sched_setattr(uattr: 0x7ffd8dcd8df0) = -1 EINVAL Invalid argument
  [root@jouet c]#

Now to figure out the reason for this EINVAL.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-tyot2n7e48zm8pdw8tbcm3sl@git.kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>