[lttng-dev] How much shared memory is used by LTTng (UST) ?
AMITM at il.ibm.com
Wed Jul 10 09:42:01 EDT 2013
Chasing down an issue with adding some context (see
https://bugs.lttng.org/issues/579), I've encountered something that makes
me think the failures I am seeing are related to amount of shared memory
that LTTng uses...
In short - when the subbuffers have a large enough size and number, adding
things to context on a multi-core system can cause libringbuffer/shm.c in
lttng-ust to complain about "No space left on device", leading to
everything looking OK, except that the trace directory stays empty.
I am working on a 6-core (12 with HT) system that has 24GB of RAM. This is
one configuration, but we also have dual-CPU systems (i.e. 12 cores / 24
with HT) with 96GB.
I am using 16 subbuffers of 256KB. In this setup, I have no problem adding
procname, vpid and vtid to the context.
When I tried the same on the 12-core dual-CPU system, it failed as
explained above. I tried reducing the subbuffer sizes to 64KB, and the
So - how can I tell how much shared memory LTTng wants, and - if you know
- how can I configure my system to allow more than the default?
IBM XIV - Storage Reinvented
XIV-NAS Development Team
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