• Joel Fernandes (Google)'s avatar
    tracing: Reorder display of TGID to be after PID · 36244e3a
    Joel Fernandes (Google) authored
    commit f8494fa3 upstream.
    
    Currently ftrace displays data in trace output like so:
    
                                           _-----=> irqs-off
                                          / _----=> need-resched
                                         | / _---=> hardirq/softirq
                                         || / _--=> preempt-depth
                                         ||| /     delay
                TASK-PID   CPU    TGID   ||||    TIMESTAMP  FUNCTION
                   | |       |      |    ||||       |         |
                bash-1091  [000] ( 1091) d..2    28.313544: sched_switch:
    
    However Android's trace visualization tools expect a slightly different
    format due to an out-of-tree patch patch that was been carried for a
    decade, notice that the TGID and CPU fields are reversed:
    
                                           _-----=> irqs-off
                                          / _----=> need-resched
                                         | / _---=> hardirq/softirq
                                         || / _--=> preempt-depth
                                         ||| /     delay
                TASK-PID    TGID   CPU   ||||    TIMESTAMP  FUNCTION
                   | |        |      |   ||||       |         |
                bash-1091  ( 1091) [002] d..2    64.965177: sched_switch:
    
    From kernel v4.13 onwards, during which TGID was introduced, tracing
    with systrace on all Android kernels will break (most Android kernels
    have been on 4.9 with Android patches, so this issues hasn't been seen
    yet). From v4.13 onwards things will break.
    
    The chrome browser's tracing tools also embed the systrace viewer which
    uses the legacy TGID format and updates to that are known to be
    difficult to make.
    
    Considering this, I suggest we make this change to the upstream kernel
    and backport it to all Android kernels. I believe this feature is merged
    recently enough into the upstream kernel that it shouldn't be a problem.
    Also logically, IMO it makes more sense to group the TGID with the
    TASK-PID and the CPU after these.
    
    Link: http://lkml.kernel.org/r/20180626000822.113931-1-joel@joelfernandes.org
    
    Cc: jreck@google.com
    Cc: tkjos@google.com
    Cc: stable@vger.kernel.org
    Fixes: 441dae8f ("tracing: Add support for display of tgid in trace output")
    Signed-off-by: 's avatarJoel Fernandes (Google) <joel@joelfernandes.org>
    Signed-off-by: 's avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
    Signed-off-by: 's avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    36244e3a