Linus,
Joel Fernandes asked to add a feature in tracing that Android had its
own patch internally for. I took it back in 4.13. Now he realizes that
he had a mistake, and swapped the values from what Android had. This
means that the old Android tools will break when using a new kernel
that has the new feature on it.
The options are:
1. To swap it back to what Android wants.
2. Add a command line option or something to do the swap
3. Just let Android carry a patch that swaps it back
Since it requires setting a tracing option to enable this anyway,
I doubt there are other users of this than Android. Thus, I've
decided to take option 1. If someone else is actually depending on the
order that is in the kernel, then we will have to revert this change
and go to option 2 or 3.
Please pull the latest trace-v4.18-rc3-3 tree, which can be found at:
git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
trace-v4.18-rc3-3
Tag SHA1: 98d877a3a308950afaaf28a0b55699726b45ad7a
Head SHA1: f8494fa3dd10b52eab47a9666a8bc34719a129aa
Joel Fernandes (Google) (1):
tracing: Reorder display of TGID to be after PID
----
kernel/trace/trace.c | 8 ++++----
kernel/trace/trace_output.c | 5 +++--
2 files changed, 7 insertions(+), 6 deletions(-)
---------------------------
commit f8494fa3dd10b52eab47a9666a8bc34719a129aa
Author: Joel Fernandes (Google) <j...@joelfernandes.org>
Date: Mon Jun 25 17:08:22 2018 -0700
tracing: Reorder display of TGID to be after PID
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-j...@joelfernandes.org
Cc: jr...@google.com
Cc: tk...@google.com
Cc: sta...@vger.kernel.org
Fixes: 441dae8f2f29 ("tracing: Add support for display of tgid in trace
output")
Signed-off-by: Joel Fernandes (Google) <j...@joelfernandes.org>
Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org>
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index f054bd6a1c66..87cf25171fb8 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3365,8 +3365,8 @@ static void print_func_help_header(struct trace_buffer
*buf, struct seq_file *m,
print_event_info(buf, m);
- seq_printf(m, "# TASK-PID CPU# %s TIMESTAMP
FUNCTION\n", tgid ? "TGID " : "");
- seq_printf(m, "# | | | %s | |\n",
tgid ? " | " : "");
+ seq_printf(m, "# TASK-PID %s CPU# TIMESTAMP
FUNCTION\n", tgid ? "TGID " : "");
+ seq_printf(m, "# | | %s | | |\n",
tgid ? " | " : "");
}
static void print_func_help_header_irq(struct trace_buffer *buf, struct
seq_file *m,
@@ -3386,9 +3386,9 @@ static void print_func_help_header_irq(struct
trace_buffer *buf, struct seq_file
tgid ? tgid_space : space);
seq_printf(m, "# %s||| / delay\n",
tgid ? tgid_space : space);
- seq_printf(m, "# TASK-PID CPU#%s|||| TIMESTAMP
FUNCTION\n",
+ seq_printf(m, "# TASK-PID %sCPU# |||| TIMESTAMP
FUNCTION\n",
tgid ? " TGID " : space);
- seq_printf(m, "# | | | %s|||| | |\n",
+ seq_printf(m, "# | | %s | |||| | |\n",
tgid ? " | " : space);
}
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 90db994ac900..1c8e30fda46a 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -594,8 +594,7 @@ int trace_print_context(struct trace_iterator *iter)
trace_find_cmdline(entry->pid, comm);
- trace_seq_printf(s, "%16s-%-5d [%03d] ",
- comm, entry->pid, iter->cpu);
+ trace_seq_printf(s, "%16s-%-5d ", comm, entry->pid);
if (tr->trace_flags & TRACE_ITER_RECORD_TGID) {
unsigned int tgid = trace_find_tgid(entry->pid);
@@ -606,6 +605,8 @@ int trace_print_context(struct trace_iterator *iter)
trace_seq_printf(s, "(%5d) ", tgid);
}
+ trace_seq_printf(s, "[%03d] ", iter->cpu);
+
if (tr->trace_flags & TRACE_ITER_IRQ_INFO)
trace_print_lat_fmt(s, entry);
