----- Original Message ----- > From: "Daniel Thibault" <[email protected]> > To: [email protected] > Cc: "mathieu desnoyers ([email protected])" > <[email protected]> > Sent: Wednesday, April 16, 2014 3:12:27 PM > Subject: RE: [lttng-dev] memory usage depending on number and size of > subbuffers > > ---------------------------------------------------------------------- > >> Date: Wed, 16 Apr 2014 18:22:42 +0200 > >> From: S?bastien Barth?l?my <[email protected]> > >> > >> LTTng uses more memory than I expected. On the simple experiment below one > >> can see that the "cached" memory increases by > >> > >> subbuf_size*num_cpu*(num_subbuf+1) > >> > >> That's not a big deal, but I did not expect the "+1". > >> > >> Does somebody know where it comes from? > > > Date: Wed, 16 Apr 2014 17:32:39 +0000 (UTC) > > From: Mathieu Desnoyers <[email protected]> > > It is the extra sub-buffer needed for reading a sub-buffer while the > > other sub-buffers are written into. It's needed for snapshotting > > data while tracing is active. > > > > Mathieu > > If I'm not mistaken, the "passing sub-buffer" is used in overwrite mode > (as opposed to discard mode), not especially for snapshot mode. It is in > fact possible to run in snapshot+discard mode, although that may not be > very useful in most use cases. Can you confirm, Mathieu?
While theoretically possible, I'm not even sure if we allow it, because it's pretty much useless. But I suspect one could indeed force a channel in discard mode for a snapshot session. David, can you confirm ? Thanks, Mathieu > > Daniel U. Thibault > Protection des systèmes et contremesures (PSC) | Systems Protection & > Countermeasures (SPC) > Cyber sécurité pour les missions essentielles (CME) | Mission Critical Cyber > Security (MCCS) > R & D pour la défense Canada - Valcartier (RDDC Valcartier) | Defence R&D > Canada - Valcartier (DRDC Valcartier) > 2459 route de la Bravoure > Québec QC G3J 1X5 > CANADA > Vox : (418) 844-4000 x4245 > Fax : (418) 844-4538 > NAC : 918V QSDJ <http://www.travelgis.com/map.asp?addr=918V%20QSDJ> > Gouvernement du Canada | Government of Canada > <http://www.valcartier.drdc-rddc.gc.ca/> > -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com _______________________________________________ lttng-dev mailing list [email protected] http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
