Re: [EXT] [PATCH v3 5/9] trace: fix dynamically enabling trace points

[David Marchand <david.marchand@redhat.com>]

On Fri, Oct 14, 2022 at 6:27 AM Jerin Jacob <jerinjacobk@gmail.com> wrote:
>
> On Fri, Oct 14, 2022 at 12:41 AM David Marchand
> <david.marchand@redhat.com> wrote:
> >
> > On Thu, Oct 13, 2022 at 7:07 PM Harman Kalra <hkalra@marvell.com> wrote:
> > > >
> > > > With the whole traces fixes series applied first, then the new "trace:
> > > > take live traces via telemetry" patch applied, I can't reproduce your issue.
> > > >
> > > >
> > >
> > > Yes, you replicated the same scenario what I tried.
> > > Sorry, I realized that actually it's not an issue, traces generated after /trace/save are getting
> > > appended but in the same file (timestamped on /trace/save) on rte_eal_cleanup().
> > >
> > > I assumed that trace dir generated with a timestamp will include all the trace points emitted
> > > before that timestamp. But in the above scenario same  trace dir includes trace points emitted
> > > after this timestamp. I think this is bit confusing. Shall we add a logic where if already_done is
> > > set, rename the original trace dir to latest timestamp?
> >
> > Afaiu, the behavior before this series was the same.
> > An application calling rte_trace_save() would always save to a single directory.
> > One thing that changed though is that the directory is timestamped
> > with the time of the first call to rte_trace_save.
> > Before the seriesn the timestamp was based on the time when the trace
> > subsystem was initialised.
> >
> >
> > We can go with what you describe (which makes sense to me).
> > But I'd like to get a ack from traces maintainers before looking into it.
>
> IMO, We can remove "already_done" logic, whenever, rte_trace_save()
> called, it creates
> the directory of that timestamp and copies the trace buffers. Since we
> have "overwrite" and "discard"
> modes, it is better to not add "already_done" dogic in rte_trace_save().

Well, it's a bit more difficult than just removing already_done.

Before my changes, the timestamp was decided and the directory created
once and for all at init.
On the other hand, every trace_mkdir() call resulted in a
trace_dir_update() call.
--> /trace/save
{"/trace/save": {"Status": "OK", "Path":
"/home/dmarchan/dpdk-traces/rte-2022-10-14-AM-08-39-37"}}
--> /trace/save
{"/trace/save": {"Status": "OK", "Path":
"/home/dmarchan/dpdk-traces/rte-2022-10-14-AM-08-39-37rte-2022-10-14-AM-08-39-38"}}

I prototyped a change (which deserves a separate patch).
Testing it, there is still one corner case when calling
rte_trace_save() twice in the same minute:
--> /trace/save
{"/trace/save": {"Status": "OK", "Path":
"/home/dmarchan/dpdk-traces/rte-2022-10-14-AM-10-11-19"}}
--> /trace/save
{"/trace/save": {"Status": "KO", "Path":
"/home/dmarchan/dpdk-traces/rte-2022-10-14-AM-10-11-19"}}

EAL: Trace dir: /home/dmarchan/dpdk-traces/rte-2022-10-14-AM-10-11-19
EAL: trace_mkdir():321 mkdir
/home/dmarchan/dpdk-traces/rte-2022-10-14-AM-10-11-19 failed [File
exists]

What do you suggest for this?


-- 
David Marchand