• Daniel Bristot de Oliveira's avatar
    tools lib traceevent: Fix prev/next_prio for deadline tasks · 07485918
    Daniel Bristot de Oliveira authored
    Currently, the sched:sched_switch tracepoint reports deadline tasks with
    priority -1. But when reading the trace via perf script I've got the
    following output:
    
      # ./d & # (d is a deadline task, see [1])
      # perf record -e sched:sched_switch -a sleep 1
      # perf script
          ...
             swapper     0 [000]  2146.962441: sched:sched_switch: swapper/0:0 [120] R ==> d:2593 [4294967295]
                   d  2593 [000]  2146.972472: sched:sched_switch: d:2593 [4294967295] R ==> g:2590 [4294967295]
    
    The task d reports the wrong priority [4294967295]. This happens because
    the "int prio" is stored in an unsigned long long val. Although it is
    set as a %lld, as int is shorter than unsigned long long,
    trace_seq_printf prints it as a positive number.
    
    The fix is just to cast the val as an int, and print it as a %d,
    as in the sched:sched_switch tracepoint's "format".
    
    The output with the fix is:
    
      # ./d &
      # perf record -e sched:sched_switch -a sleep 1
      # perf script
          ...
             swapper     0 [000]  4306.374037: sched:sched_switch: swapper/0:0 [120] R ==> d:10941 [-1]
                   d 10941 [000]  4306.383823: sched:sched_switch: d:10941 [-1] R ==> swapper/0:0 [120]
    
    [1] d.c
    
     ---
      #include <stdio.h>
      #include <unistd.h>
      #include <sys/syscall.h>
      #include <linux/types.h>
      #include <linux/sched.h>
    
      struct sched_attr {
    	__u32 size, sched_policy;
    	__u64 sched_flags;
    	__s32 sched_nice;
    	__u32 sched_priority;
    	__u64 sched_runtime, sched_deadline, sched_period;
      };
    
      int sched_setattr(pid_t pid, const struct sched_attr *attr, unsigned int flags)
      {
    	return syscall(__NR_sched_setattr, pid, attr, flags);
      }
    
      int main(void)
      {
    	struct sched_attr attr = {
    		.size		= sizeof(attr),
    		.sched_policy	= SCHED_DEADLINE, /* This creates a 10ms/30ms reservation */
    		.sched_runtime	= 10 * 1000 * 1000,
    		.sched_period	= attr.sched_deadline = 30 * 1000 * 1000,
    	};
    
    	if (sched_setattr(0, &attr, 0) < 0) {
    		perror("sched_setattr");
    		return -1;
    	}
    
    	for(;;);
      }
     ---
    
    Committer notes:
    
    Got the program from the provided URL, http://bristot.me/lkml/d.c,
    trimmed it and included in the cset log above, so that we have
    everything needed to test it in one place.
    Signed-off-by: default avatarDaniel Bristot de Oliveira <bristot@redhat.com>
    Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
    Tested-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
    Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Link: http://lkml.kernel.org/r/866ef75bcebf670ae91c6a96daa63597ba981f0d.1483443552.git.bristot@redhat.comSigned-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
    07485918
plugin_sched_switch.c 4.38 KB