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Date: Thu, 7 Apr 2011 13:22:30 -0700 From: David Sharp <dhsharp@...gle.com> To: Frederic Weisbecker <fweisbec@...il.com> Cc: Vaibhav Nagarnaik <vnagarnaik@...gle.com>, Paul Menage <menage@...gle.com>, Li Zefan <lizf@...fujitsu.com>, Stephane Eranian <eranian@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, Steven Rostedt <rostedt@...dmis.org>, Michael Rubin <mrubin@...gle.com>, Ken Chen <kenchen@...gle.com>, linux-kernel@...r.kernel.org, containers@...ts.linux-foundation.org Subject: Re: [RFC] tracing: Adding cgroup aware tracing functionality On Thu, Apr 7, 2011 at 5:06 AM, Frederic Weisbecker <fweisbec@...il.com> wrote: > On Wed, Apr 06, 2011 at 08:17:33PM -0700, Vaibhav Nagarnaik wrote: >> On Wed, Apr 6, 2011 at 6:33 PM, Frederic Weisbecker <fweisbec@...il.com> wrote: >> > On Wed, Apr 06, 2011 at 11:50:21AM -0700, Vaibhav Nagarnaik wrote: >> >> All >> >> The cgroup functionality is being used widely in different scenarios. It also >> >> is being integrated with other parts of kernel to take advantage of its >> >> features. One of the areas that is not yet aware of cgroup functionality is >> >> the ftrace framework. >> >> >> >> Although ftrace provides a way to filter based on PIDs of tasks to be traced, >> >> it is restricted to specific tracers, like function tracer. Also it becomes >> >> difficult to keep track of all PIDs in a dynamic environment with processes >> >> being created and destroyed in a short amount of time. >> >> >> >> An application that creates many processes/tasks is convenient to track and >> >> control with cgroups, but it is difficult to track these processes for the >> >> purposes of tracing. And if child processes are moved to another cgroup, it >> >> makes sense to trace only the original cgroup. >> >> >> >> This proposal is to create a file in the tracing directory called >> >> set_trace_cgroup to which a user can write the path of an active cgroup, one >> >> at a time. If no cgroups are specified, no filtering is done and all tasks are >> >> traced. When a cgroup path is added in, it sets a boolean tracing_enabled for >> >> the enabled cgroup in all the hierarchies, which enables tracing for all the >> >> assigned tasks under the specified cgroup. >> >> >> >> Though creating a new file in the directory is not desirable, but this >> >> interface seems the most appropriate change required to implement the new >> >> feature. >> >> >> >> This tracing_enabled flag is also exported in the cgroupfs directory structure >> >> which can be turned on/off for a specific hierarchy/cgroup combination. This >> >> gives control to enable/disable tracing over a cgroup in a specific hierarchy >> >> only. >> >> >> >> This gives more fine-grained control over the tasks being traced. I would like >> >> to know your thoughts on this interface and the approach to make tracing >> >> cgroup aware. >> > >> > So I have to ask, why can't you use perf events to do tracing limited on cgroups? >> > It has this cgroup context awareness. Perf doesn't have the same latency characteristics as ftrace. It costs a full microsecond for every trace event. https://lkml.org/lkml/2010/10/28/261 It's possible these results need to be updated. Has any effort been made to improve the tracing latency of perf? >> The perf event cgroup awareness comes from creating a different hierarchy for >> perf events. When the events and the current task's cgroup match, the events >> are logged. So the changes are pretty specific to the perf events. >> >> Even in the case where changes are made to handle trace events, the interface >> files are still needed. The interface used to specify perf events uses the >> perf_event syscall which isn't available to specify trace events. >> >> This is based on my limited understanding of the perf_events cgroup awareness >> patch. Please correct me if I am missing anything. > > > Ah but perf events can do much more than counting and sampling > hardware events. Trace events can be used as perf events too. > > List the events: > > perf list -e tracepoints > > List of pre-defined events (to be used in -e): > > skb:kfree_skb [Tracepoint event] > skb:consume_skb [Tracepoint event] > skb:skb_copy_datagram_iovec [Tracepoint event] > net:net_dev_xmit [Tracepoint event] > net:net_dev_queue [Tracepoint event] > net:netif_receive_skb [Tracepoint event] > net:netif_rx [Tracepoint event] > napi:napi_poll [Tracepoint event] > scsi:scsi_dispatch_cmd_start [Tracepoint event] > scsi:scsi_dispatch_cmd_error [Tracepoint event] > scsi:scsi_dispatch_cmd_done [Tracepoint event] > scsi:scsi_dispatch_cmd_timeout [Tracepoint event] > scsi:scsi_eh_wakeup [Tracepoint event] > drm:drm_vblank_event [Tracepoint event] > drm:drm_vblank_event_queued [Tracepoint event] > drm:drm_vblank_event_delivered [Tracepoint event] > block:block_rq_abort [Tracepoint event] > block:block_rq_requeue [Tracepoint event] > block:block_rq_complete [Tracepoint event] > block:block_rq_insert [Tracepoint event] > etc... > > > Trace sched switch events: > > perf record -e sched:sched_switch -a > ^C > > > Print them: > > perf script > > swapper 0 [000] 1132.964598: sched_switch: prev_comm=swapper prev_pid=0 prev_prio=120 prev_state=R ==> next_comm > kworker/0:1 4358 [000] 1132.964641: sched_switch: prev_comm=kworker/0:1 prev_pid=4358 prev_prio=120 prev_state=S ==> ne > syslogd 2703 [000] 1132.964720: sched_switch: prev_comm=syslogd prev_pid=2703 prev_prio=120 prev_state=D ==> next_c > swapper 0 [000] 1132.965100: sched_switch: prev_comm=swapper prev_pid=0 prev_prio=120 prev_state=R ==> next_comm > perf 4725 [001] 1132.965178: sched_switch: prev_comm=perf prev_pid=4725 prev_prio=120 prev_state=D ==> next_comm > swapper 0 [001] 1132.965227: sched_switch: prev_comm=kworker/0:0 prev_pid=0 prev_prio=120 prev_state=R ==> next_ > perf 4725 [001] 1132.965246: sched_switch: prev_comm=perf prev_pid=4725 prev_prio=120 prev_state=D ==> next_comm > etc... > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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