On 2015/04/23 01:14PM, Michael Ellerman wrote:
> On Wed, 2015-04-22 at 10:48 +0530, Naveen N. Rao wrote:
> > On 2015/04/21 09:25AM, Steven Rostedt wrote:
> > > On Tue, 21 Apr 2015 16:33:36 +0530
> > > "Naveen N. Rao" <naveen.n....@linux.vnet.ibm.com> wrote:
> > >
> > > > Add a new powerpc-specific trace clock using the timebase register,
> > > > similar to x86-tsc. This gives us a fast, monotonic, cross-cpu clock
> > > > for trace entries and can be used to correlate events across cpus as
> > > > well as across hypervisor and guest (assuming it is not a migrated guest
> > > > with a non-zero tb_offset).
> > > >
> > > > Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
> > > > ---
> > > > I have followed the approach used by x86-tsc here, but we could get rid
> > > > of
> > > > trace_clock.c if we directly use get_tb() with perhaps the notrace
> > > > annotation.
> > > > Would that be preferable?
> > > >
> > >
> > > Probably. But all clocks used by tracing should be marked by notrace.
> > > Don't just wrap it with a notrace. But looking at the code, it seems
> > > that get_tb() is a static inline, which wont work as a pointer. Seems
> > > you still need the indirect function call.
> > >
> > > Note, all "inline" functions are notrace by default, so you do not need
> > > to add any notrace annotation to an inlined function.
> >
> > Steve,
> > Thanks for the clarification - the current approach is better in that
> > case.
> >
> > Paul, Mike,
> > Can you please let me know your thoughts on this?
>
> What is the value in adding a powerpc specific clock, which requires educating
> people to use it, vs just using the global clock?
Hi Michael,
There are two reasons:
- One, using the timebase register gives us a very fast (just one
instruction) hardware clock source for trace entries compared to the
global clock.
- Two, using the timebase values allows us to correlate trace events
across hypervisor and guest, which is not possible using the other
trace clocks. [With migrated guests, there could be a non-zero
tb_offset which we may also want to make available to userspace in
some manner. Any suggestions?]
This will show up as an additional trace clock and can be selected if
one wishes to use it. As an example:
[root@rhel7-img ~]# cd /sys/kernel/debug/tracing
[root@rhel7-img tracing]# cat trace_clock
[local] global counter uptime perf mono ppc-tb
[root@rhel7-img tracing]# head -30 trace
# tracer: nop
#
# entries-in-buffer/entries-written: 534/534 #P:4
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
tuned-1080 [003] .... 1108.294606: sys_select -> 0x0
tuned-1080 [003] .... 1108.294655: sys_select(n: 0, inp: 0, outp:
0, exp: 0, tvp: 3fff9b7fcdf0)
bash-2732 [001] .... 1108.336317: sys_write -> 0x6
bash-2732 [001] .... 1108.336321: sys_dup2(oldfd: a, newfd: 1)
bash-2732 [001] .... 1108.336323: sys_dup2 -> 0x1
bash-2732 [001] .... 1108.336327: sys_fcntl(fd: a, cmd: 1, arg: 0)
bash-2732 [001] .... 1108.336328: sys_fcntl -> 0x1
bash-2732 [001] .... 1108.336330: sys_close(fd: a)
bash-2732 [001] .... 1108.336330: sys_close -> 0x0
bash-2732 [001] .... 1108.336340: sys_rt_sigprocmask(how: 0,
nset: 0, oset: 10146e48, sigsetsize: 8)
bash-2732 [001] .... 1108.336341: sys_rt_sigprocmask -> 0x0
bash-2732 [001] .... 1108.336342: sys_rt_sigaction(sig: 2, act:
3fffc17d8e20, oact: 3fffc17d8d80, sigsetsize: 8)
bash-2732 [001] .... 1108.336343: sys_rt_sigaction -> 0x0
bash-2732 [001] .... 1108.336352: sys_rt_sigprocmask(how: 0,
nset: 0, oset: 10146e48, sigsetsize: 8)
bash-2732 [001] .... 1108.336352: sys_rt_sigprocmask -> 0x0
bash-2732 [001] .... 1108.336476: sys_write(fd: 1, buf:
3fff7f370000, count: 2d)
bash-2732 [001] .... 1108.336484: sys_write -> 0x2d
bash-2732 [001] .... 1108.336512: sys_rt_sigprocmask(how: 0,
nset: 3fffc17d7c40, oset: 3fffc17d7cc0, sigsetsize: 8)
bash-2732 [001] .... 1108.336513: sys_rt_sigprocmask -> 0x0
[root@rhel7-img tracing]# echo ppc-tb > trace_clock
[root@rhel7-img tracing]# cat trace_clock
local global counter uptime perf mono [ppc-tb]
[root@rhel7-img tracing]# echo 0 > trace
[root@rhel7-img tracing]# head -30 trace
# tracer: nop
#
# entries-in-buffer/entries-written: 396/396 #P:4
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
bash-2732 [002] .... 34405585249004: sys_write -> 0x7
bash-2732 [002] .... 34405585251162: sys_dup2(oldfd: a, newfd: 1)
bash-2732 [002] .... 34405585252104: sys_dup2 -> 0x1
bash-2732 [002] .... 34405585253774: sys_fcntl(fd: a, cmd: 1, arg:
0)
bash-2732 [002] .... 34405585254385: sys_fcntl -> 0x1
bash-2732 [002] .... 34405585255051: sys_close(fd: a)
bash-2732 [002] .... 34405585255589: sys_close -> 0x0
bash-2732 [002] .... 34405585260898: sys_rt_sigprocmask(how: 0,
nset: 0, oset: 10146e48, sigsetsize: 8)
bash-2732 [002] .... 34405585261482: sys_rt_sigprocmask -> 0x0
bash-2732 [002] .... 34405585262339: sys_rt_sigaction(sig: 2, act:
3fffc17d8e20, oact: 3fffc17d8d80, sigsetsize: 8)
bash-2732 [002] .... 34405585262927: sys_rt_sigaction -> 0x0
bash-2732 [002] .... 34405585267215: sys_rt_sigprocmask(how: 0,
nset: 0, oset: 10146e48, sigsetsize: 8)
bash-2732 [002] .... 34405585267690: sys_rt_sigprocmask -> 0x0
bash-2732 [002] .... 34405585345924: sys_write(fd: 1, buf:
3fff7f370000, count: 2d)
bash-2732 [002] .n.. 34405585350359: sys_write -> 0x2d
bash-2732 [002] .... 34405585428096: sys_rt_sigprocmask(how: 0,
nset: 3fffc17d7c40, oset: 3fffc17d7cc0, sigsetsize: 8)
bash-2732 [002] .... 34405585447011: sys_rt_sigprocmask -> 0x0
bash-2732 [002] .... 34405585447956: sys_ioctl(fd: ff, cmd:
80047476, arg: 3fffc17d7c08)
bash-2732 [002] .... 34405585449451: sys_ioctl -> 0x0
- Naveen
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