[lttng-dev] [tracecompass-dev] Scalability

[Philippe Proulx]

On Wed, Mar 13, 2019 at 8:46 AM Doug Schaefer <dschaefer at blackberry.com> wrote:
>
> Very cool. Would explicitly setting the byte order for each field be a short term workaround?

You found a very specific scenario highlighting this bug.

Some field types are copied behind the scenes for resolving purposes.
This is done in bt_ctf_stream_class_add_event_class() and
bt_ctf_writer_create_stream(). The effective byte order of the original
(`data_length_type` for example) remains unset, while the internal copy
is set. However you use the originals to create fields.

Without the patch, a temporary fix would be to put all the field type
references and get the copies (which have the correct byte order) using
bt_ctf_event_class_get_field_by_name() and
bt_ctf_field_sequence_get_field() _after_ calling
bt_ctf_writer_create_stream() in your specific case.

Phil

>
> Sent from my BlackBerry - the most secure mobile device - via the Rogers Network
> From: eeppeliteloop at gmail.com
> Sent: March 13, 2019 8:30 AM
> To: matthew.khouzam at ericsson.com
> Cc: jonathan.rajotte-julien at efficios.com; dschaefer at blackberry.com; tracecompass-dev at eclipse.org; lttng-dev at lists.lttng.org
> Subject: Re: [lttng-dev] [tracecompass-dev] Scalability
>
> On Wed, Mar 13, 2019 at 8:13 AM Matthew Khouzam
> <matthew.khouzam at ericsson.com> wrote:
> >
> > Hi Doug & Efficios,
> >
> >
> > I suspect the issue is with libbabeltrace-ctf. When opening the trace in Trace Compass, it failed saying the sequence was 2gb big. When opening in babeltrace, it OOMed with 2gb allocations. When opening with a hex editor, I saw 2gb allocations.
>
> Yes, byte order issues. Here's the fix:
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_efficios_babeltrace_pull_103&d=DwIFaQ&c=yzoHOc_ZK-sxl-kfGNSEvlJYanssXN3q-lhj0sp26wE&r=NrrbvTHWa2Nbp_kAN0Hl1o3lM1WAwSes64uBjxjNhMc&m=mro2UhDCczUi0qeroLQR1acWtiyKnR0DeQlLZcufM9M&s=0QPaQrHAx605SVgAPeaZnF264NFCA44uOkcXdbV5dpA&e=>.
>
> Phil
>
> >
> >
> > On another subject, fixing the trace made it scale well in both babeltrace and Trace Compass.
> >
> >
> > I don't know why, data_length writes the wrong data. Hope this helps all parties.
> >
> >
> > BR,
> >
> > Matthew
> >
> > ________________________________
> > From: tracecompass-dev-bounces at eclipse.org <tracecompass-dev-bounces at eclipse.org> on behalf of Doug Schaefer <dschaefer at blackberry.com>
> > Sent: Tuesday, March 12, 2019 2:50:29 PM
> > To: jonathan.rajotte-julien at efficios.com
> > Cc: lttng-dev at lists.lttng.org; tracecompass-dev at eclipse.org
> > Subject: Re: [tracecompass-dev] [lttng-dev] Scalability
> >
> > I have attached the C file for a generator that creates a trace that reproduces the memory issue with babeltrace. The same issue happens with a custom program in the call to add a trace to a context.
> >
> > I am using babeltrace that I get from my Ubuntu 18.04 distro. It has the version number 1.5.5.
> >
> > Thanks for the help!
> >
> > On Tue, 2019-03-12 at 15:47 +0000, Doug Schaefer wrote:
> >
> > In the thread on the tracecompass list, I also mentioned that the babeltrace utility itself ran out of memory when reading the file. That's actually my biggest worry. I got around the generator issue by flushing every 100K events.
> >
> > I'll create a quick generator that shows the same issue and post it in a bit.
> >
> > Doug.
> >
> > On Tue, 2019-03-12 at 11:34 -0400, Jonathan Rajotte-Julien wrote:
> >
> > On Tue, Mar 12, 2019 at 03:23:23PM +0000, Doug Schaefer wrote:
> >
> > It should be easy to generate a random one with the class I mentioned below
> >
> > and fill it with 16 million events.
> >
> >
> > Not if the problem is in the generator code ;).
> >
> >
> > BTW, two of the int fields are 5 and 10
> >
> > bits respectively, but I'm not sure that matters (or at least it shouldn't).
> >
> >
> > Make sure to check the endian-ness of those fields.
> >
> >
> > What class? Not sure I see any reference to any.
> >
> >
> > Since you are generating CTF the error can be in the generator code. Please
> >
> > provide either a trace reproducing the issue or a base reproducer. It will be
> >
> > much easier overall than us trying to reproduce it blindly.
> >
> >
> > Cheers.
> >
> >
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