<font size=2 face="sans-serif">That explains a lot. Our SHM space is hard
coded to 64MB, which limits me big-time.</font>
<br>
<br><font size=2 face="sans-serif">It still doesn't explain why I was able
to add procname to the context but adding also vpid and vtid failed when
the number of cores was 24 rather than 12.</font>
<br>
<br><font size=2 face="sans-serif">I mean - the formula you give (and we
use per-UID buffers) doesn't seem to be related to what's in context and
what's not...</font>
<br>
<br><font size=2 face="sans-serif">Now, on the 12 core (6+HT) system, I
would need - </font>
<br>
<br><tt><font size=2>nb_traced_users(=1) * subbuf_size(=256KB) * nr_subbuf(=16)
* nb_cpus(=12) = 1*256KB*16*16 = 48MB</font></tt>
<br>
<br><font size=2 face="sans-serif">But the same arguments worked just fine
on the 24-core system, including adding procname to context. Adding vtid
+ vpid worked on the 12-core, but failed on the 24-core system.</font>
<br>
<br><font size=2 face="sans-serif">Any ideas why?</font>
<br>
<br><font size=2 color=#000080 face="sans-serif">Amit Margalit</font>
<br><font size=2 color=#808000 face="sans-serif">IBM XIV </font><font size=2 face="sans-serif">-
<i>Storage Reinvented</i></font>
<br><font size=2 face="sans-serif">XIV-NAS Development Team</font>
<br><font size=2 face="sans-serif">Tel. 03</font><font size=2 face="Arial">-689-7774</font>
<br><font size=2 face="Arial">Fax. 03-689-7230</font>
<br>
<br>
<br>
<br><font size=1 color=#5f5f5f face="sans-serif">From:
</font><font size=1 face="sans-serif">Mathieu Desnoyers <mathieu.desnoyers@efficios.com></font>
<br><font size=1 color=#5f5f5f face="sans-serif">To:
</font><font size=1 face="sans-serif">Amit Margalit/Israel/IBM@IBMIL</font>
<br><font size=1 color=#5f5f5f face="sans-serif">Cc:
</font><font size=1 face="sans-serif">lttng-dev@lists.lttng.org</font>
<br><font size=1 color=#5f5f5f face="sans-serif">Date:
</font><font size=1 face="sans-serif">07/10/2013 04:59 PM</font>
<br><font size=1 color=#5f5f5f face="sans-serif">Subject:
</font><font size=1 face="sans-serif">Re: [lttng-dev]
How much shared memory is used by LTTng (UST) ?</font>
<br>
<hr noshade>
<br>
<br>
<br><tt><font size=2>* Amit Margalit (AMITM@il.ibm.com) wrote:<br>
> Hi,<br>
> <br>
> Chasing down an issue with adding some context (see <br>
> </font></tt><a href=https://bugs.lttng.org/issues/579><tt><font size=2>https://bugs.lttng.org/issues/579</font></tt></a><tt><font size=2>),
I've encountered something that makes <br>
> me think the failures I am seeing are related to amount of shared
memory <br>
> that LTTng uses...<br>
> <br>
> In short - when the subbuffers have a large enough size and number,
adding <br>
> things to context on a multi-core system can cause libringbuffer/shm.c
in <br>
> lttng-ust to complain about "No space left on device", leading
to <br>
> everything looking OK, except that the trace directory stays empty.<br>
> <br>
> I am working on a 6-core (12 with HT) system that has 24GB of RAM.
This is <br>
> one configuration, but we also have dual-CPU systems (i.e. 12 cores
/ 24 <br>
> with HT) with 96GB.<br>
> <br>
> I am using 16 subbuffers of 256KB. In this setup, I have no problem
adding <br>
> procname, vpid and vtid to the context.<br>
> <br>
> When I tried the same on the 12-core dual-CPU system, it failed as
<br>
> explained above. I tried reducing the subbuffer sizes to 64KB, and
the <br>
> problem disappeared.<br>
> <br>
> So - how can I tell how much shared memory LTTng wants, and - if you
know <br>
> - how can I configure my system to allow more than the default?<br>
<br>
First thing, try using per-uid buffers rather than the 2.2 default<br>
(per-pid buffers).<br>
<br>
If you do that, then you will need:<br>
nb_traced_users * subbuf_size * nr_subbuf * nb_cpus as shm
space.<br>
<br>
If you stay with per-pid buffers, then you need<br>
nb_processes * subbuf_size * nr_subbuf * nb_cpus as shm space.<br>
<br>
On my system here, I notice that each shm creates files within /run/shm<br>
(this location may differ on your system). It is a tmpfs filesystem. You<br>
might want to increase its size. For instance, here, it is 1.6GB.<br>
<br>
Thanks,<br>
<br>
Mathieu<br>
<br>
> <br>
> Thanks,<br>
> <br>
> Amit Margalit<br>
> IBM XIV - Storage Reinvented<br>
> XIV-NAS Development Team<br>
> Tel. 03-689-7774<br>
> Fax. 03-689-7230<br>
> _______________________________________________<br>
> lttng-dev mailing list<br>
> lttng-dev@lists.lttng.org<br>
> </font></tt><a href="http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev"><tt><font size=2>http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev</font></tt></a><tt><font size=2><br>
<br>
<br>
-- <br>
Mathieu Desnoyers<br>
EfficiOS Inc.<br>
</font></tt><a href=http://www.efficios.com/><tt><font size=2>http://www.efficios.com</font></tt></a><tt><font size=2><br>
<br>
</font></tt>
<br>