From mboxrd@z Thu Jan 1 00:00:00 1970 From: andrew.mcdermott@windriver.com (Andrew McDermott) Date: Thu, 12 Feb 2009 11:53:16 +0000 Subject: [ltt-dev] limiting LTTng to a certain set of cores In-Reply-To: <20090211175539.GE26549@Krystal> (Mathieu Desnoyers's message of "Wed, 11 Feb 2009 12:55:39 -0500") References: <20090211175539.GE26549@Krystal> Message-ID: > * 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 : Thanks for the info! Perhaps it is something to consider for a future release. One of the issues I'm facing is that the trace is large and by large I mean I have to transfer the trace in its entirety from a remote location. If I could collect on a subset of the cores then I would have less to transfer (over my very slow link). > > 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 >> -- andy