Re: [PATCH 5/7] trace-cmd: Added user configured clock to the record context

[Slavomir Kaslev <slavomir.kaslev@gmail.com>]

On Tue, Jan 22, 2019 at 3:44 PM Tzvetomir Stoyanov <tstoyanov@vmware.com> wrote:
>
> On Mon, Jan 21, 2019 at 11:19 AM Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> > On Wed, 16 Jan 2019 21:18:36 +0200
> > Tzvetomir Stoyanov <tstoyanov@vmware.com> wrote:
> >
> > > Store the user configured clock (if any) in the record context,
> > > struct common_record_context. The clock is going to be used when
> > > synchronizing timestamps with remote tracing machine.
> > > ---
> > >  tracecmd/trace-record.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > >
> > > diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
> > > index f7349eb..900d0d4 100644
> > > --- a/tracecmd/trace-record.c
> > > +++ b/tracecmd/trace-record.c
> > > @@ -227,6 +227,7 @@ struct common_record_context {
> > >       int topt;
> > >       int do_child;
> > >       int run_command;
> > > +     char *clock;
> > >  };
> > >
> > >  static void add_reset_file(const char *file, const char *val, int prio)
> > > @@ -5183,6 +5184,7 @@ static void parse_record_options(int argc,
> > >                       break;
> > >               case 'C':
> > >                       ctx->instance->clock = optarg;
> > > +                     ctx->clock = optarg;
> >
> > Hmm, this can cause an issue. The first thing I have to ask is, why
> > can't we use ctx->instance->clock. I'm sure the answer is that we are
> > adding more than one clock. But this begs the question, which clock
> > should be use, if there are more than one clock to add?
> >
> > I think this patch is not needed. In the last patch, test if
> > ctx->instance->clock exists, and if not, we search the other instances
> > for a clock to use. Or something else that doesn't make which clock to
> > use ambiguous.
>
> Ok, I'll remove it and will search for the first ctx->instance->clock instead.
> Current algorithm assumes that only one clock is used, and it is the
> same in both
> host and guest contexts. We should think how to handle the case with
> multiple instances,
> each one with different clock. I do not know, how instances are
> written in the trace.dat file,
> is there a different time offset option in the file, per instance ?

Each instance goes into a separate file (by default "trace-$(name).dat").

For guest instances, this command
$ trace-cmd record -A guest0 -e irq -e sched -A guest1 -e irq -e sched

creates two trace files:
-rw-r--r-- 1 4.8M Jan 22 16:06 trace-guest0.dat
-rw-r--r-- 1 7.4M Jan 22 16:06 trace-guest1.dat

Cheers,

- Slavi