From mboxrd@z Thu Jan 1 00:00:00 1970 From: compudj@krystal.dyndns.org (Mathieu Desnoyers) Date: Wed, 11 Feb 2009 12:55:39 -0500 Subject: [ltt-dev] limiting LTTng to a certain set of cores In-Reply-To: References: Message-ID: <20090211175539.GE26549@Krystal> * Andrew McDermott (andrew.mcdermott at windriver.com) wrote: > > Is there an easy way to limit LTTng to trace a specified set of cores > only? I ask because in some 64+ core systems the data set collected > becomes too large for analysis and the tasks to be analyzed are always > bound to certain cores (using affinity). > > I'm anticipating that this would require changes to LTTng - what I would > like to know is how invasive those changes would need to be. > Hi Andrew, Basically, this could be done on a per tracing-session/per-channel basis by adding an "active core" bit mask to test within ltt_vtrace and ltt_serialize_data, in the loop where it iterates on active traces and calls the "filter" callback. This bitmask would sit within the channel structure. Setting the active cores should be added to the debugfs interface : People would do : echo tracename > /mnt/debugfs/ltt/setup_trace echo CPUNR > /mnt/debugfs/ltt/control/tracename/channel/channelname/cpus cat /mnt/debugfs/ltt/control/tracename/channel/channelname/cpus ... Maybe we should replace the "enable" test by a cpu mask test with all cpus active to save some cycles... And I don't particularly care about the exact debugfs file interface (file name, the way the cpus are listed). Ideally if we can find somewhere else in the Linux kernel where it is already done, that would be a great inspiration source. Thanks, Mathieu > Thanks, > Andy. > > _______________________________________________ > ltt-dev mailing list > ltt-dev at lists.casi.polymtl.ca > http://lists.casi.polymtl.ca/cgi-bin/mailman/listinfo/ltt-dev > -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68