From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751470AbdFZWtn (ORCPT ); Mon, 26 Jun 2017 18:49:43 -0400 Received: from mga02.intel.com ([134.134.136.20]:2297 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750819AbdFZWti (ORCPT ); Mon, 26 Jun 2017 18:49:38 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.39,397,1493708400"; d="scan'208";a="103912204" From: Tom Zanussi To: rostedt@goodmis.org Cc: tglx@linutronix.de, mhiramat@kernel.org, namhyung@kernel.org, vedang.patel@intel.com, linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, Tom Zanussi Subject: [PATCH 00/32] tracing: Inter-event (e.g. latency) support Date: Mon, 26 Jun 2017 17:49:00 -0500 Message-Id: X-Mailer: git-send-email 1.9.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patchset adds support for 'inter-event' quantities to the trace event subsystem. The most important example of inter-event quantities are latencies, or the time differences between two events. This is a follow-up to the initial RFC patchset and subsequent discussion at ELC. I think I've covered all the basic suggestions from both those sources - thanks to everyone who reviewed and contributed suggestions. Also, thanks to Vedang Patel for testing and providing real-user input and scripts - a number of the new patches such as extended error reporting, cpu fields, and aliases address his input directly. The current patchset has been fairly well tested and I'm not aware of any major problems with it, but there is one problem/feature to be aware of, which has to do with the fact that currently the tracing map can naturally have duplicate entries. Normally this is expected and isn't a problem for histograms without variables attached, as duplicates are merged on output. If a histogram has variables though and gets a duplicate entry, the variable associated with that record can't be trusted, since it can't be retrieved again. Luckily duplicates are normally very rare occurrences - I've never personally seen one in practice - but it does mean that you always need to check that the 'Duplicates' value on the histogram summary is 0 if that histogram has variables attached. We're currently working on a 'fix' for this that basically eliminates the possibility of duplicates, but for now the 'Duplicates' total will alert users to that rare situation should it occur. One of the main motivations for adding this capability is to provide a general-purpose base that existing existing tools such as the -RT latency_hist patchset can be built upon, while at the same time providing a simple way for users to track latencies (or any inter-event quantity) generically between any two events. Previous -RT latency_hist patchsets that take advantage of the trace event subsystem have been submitted, but they essentially hard-code special-case tracepoints and application logic in ways that can't be reused. It seemed to me that rather than providing a one-off patchset devoted specifically to generating the specific histograms in the latency_hist patchset, it should be possible to build the same functionality on top of a generic layer allowing users to do similar things for other non-latency_hist applications. In addition to preliminary patches that add some basic missing functionality such as a common ringbuffer-derived timestamp and dynamically-creatable tracepoints, the overall patchset is divided up into a few different areas that combine to produce the overall goal (The Documentation patch explains all the details): - variables and simple expressions required to calculate a latency In order to calculate a latency or any inter-event value, something from one event needs to be saved and later retrieved, and some operation such as subtraction or addition is performed on it. This means some minimal form of variables and expressions, which the first set of patches implements. Saving and retrieving events to use in a latency calculation is normally done using a hash table, and that's exactly what we have with trace event hist triggers, so that's where variables are instantiated, set, and retrieved. Basically, variables are set on one entry and retrieved and used by a 'matching' event. - 'synthetic' events, combining variables from other events The trace event interface is based on pseudo-files associated with individual events, so it wouldn't really make sense to have quantities derived from multiple events attached to any one of those events. For that reason, the patchset implements a means of combining variables from other events into a separate 'synthetic' event, which can be treated as if it were just like any other trace event in the system. - 'actions' generating synthetic events, among other things Variables and synthetic events provide the data and data structure for new events, but something still needs to actually generate an event using that data. 'Actions' are expanded to provide that capability. Though it hasn't been explicitly called as much before, the default 'action' currently for a hist trigger is to update the matching histogram entry's sum values. This patchset essentially expands that to provide a new 'onmatch.event(params)' action that can be used to have one event generate another. The mechanism is extensible to other actions, and in fact the patchset also includes another, 'onmax(var).save(field,...)' that can be used to save context whenever a value exceeds the previous maximum (something also needed by latency_hist). Here are some examples that should make things less abstract. ==== Example - wakeup latency ==== This basically implements the -RT latency_hist 'wakeup_latency' histogram using the synthetic events, variables, and actions described. The output below is from a run of cyclictest using the following command: # rt-tests/cyclictest -p 80 -n -s -t 2 What we're measuring the latency of is the time between when a thread (of cyclictest) is awakened and when it's scheduled in. To do that we add triggers to sched_wakeup and sched_switch with the appropriate variables, and on a matching sched_switch event, generate a synthetic 'wakeup_latency' event. Since it's just another trace event like any other, we can also define a histogram on that event, the output of which is what we see displayed when reading the wakeup_latency 'hist' file. First, we create a synthetic event called wakeup_latency, that creates 3 fields which will reference variables from other events: # echo 'wakeup_latency u64 lat; pid_t pid; int prio' >> \ /sys/kernel/debug/tracing/synthetic_events Next we add a trigger to sched_wakeup, which saves the value of the '$common_timestamp' when that event is hit in a variable, ts0. Note that this happens only when 'comm==cyclictest'. Also, '$common_timestamp' is a new field defined on every event (if needed - if there are no users of timestamps in a trace, timestamps won't be saved and there's no additional overhead from that). # echo 'hist:keys=pid:ts0=$common_timestamp.usecs if comm=="cyclictest"' >> \ /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger Next, we add a trigger to sched_switch. When the pid being switched to matches the pid woken up by a previous sched_wakeup event, this event grabs the ts0 variable saved on that event, takes the difference between it and the current sched_switch's $common_timestamp, and assigns it to a new 'wakeup_lat' variable. It then generates the wakeup_latency synthetic event defined earlier by 'invoking' it as a function using as parameters the wakeup_lat variable and two sched_switch event fields directly: # echo 'hist:keys=next_pid:wakeup_lat=$common_timestamp.usecs-$ts0: \ onmatch(sched.sched_wakeup).wakeup_latency($wakeup_lat,next_pid,next_prio) \ if next_comm=="cyclictest"' >> \ /sys/kernel/debug/tracing/events/sched/sched_switch/trigger Finally, all we have left to do is create a standard histogram simply naming the fields of the wakeup_latency synthetic event: # echo 'hist:keys=pid,prio,lat:sort=pid,lat' >> \ /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger At any time, we can see the histogram output by simply reading the synthetic/wakeup_latency/hist file: # cat /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/hist # event histogram # # trigger info: hist:keys=pid,prio,lat:vals=hitcount:sort=pid,lat:size=2048 [active] # { pid: 2519, prio: 120, lat: 1 } hitcount: 12 { pid: 2519, prio: 120, lat: 2 } hitcount: 671 { pid: 2519, prio: 120, lat: 3 } hitcount: 588 { pid: 2519, prio: 120, lat: 4 } hitcount: 202 { pid: 2519, prio: 120, lat: 5 } hitcount: 28 { pid: 2519, prio: 120, lat: 6 } hitcount: 13 { pid: 2519, prio: 120, lat: 7 } hitcount: 12 { pid: 2519, prio: 120, lat: 8 } hitcount: 7 { pid: 2519, prio: 120, lat: 9 } hitcount: 12 { pid: 2519, prio: 120, lat: 10 } hitcount: 11 { pid: 2519, prio: 120, lat: 11 } hitcount: 7 { pid: 2519, prio: 120, lat: 12 } hitcount: 6 { pid: 2519, prio: 120, lat: 13 } hitcount: 1 { pid: 2519, prio: 120, lat: 17 } hitcount: 1 { pid: 2519, prio: 120, lat: 18 } hitcount: 3 { pid: 2519, prio: 120, lat: 19 } hitcount: 2 { pid: 2519, prio: 120, lat: 22 } hitcount: 2 { pid: 2519, prio: 120, lat: 23 } hitcount: 1 { pid: 2519, prio: 120, lat: 24 } hitcount: 1 { pid: 2519, prio: 120, lat: 27 } hitcount: 1 { pid: 2519, prio: 120, lat: 34 } hitcount: 1 { pid: 2519, prio: 120, lat: 53 } hitcount: 1 { pid: 2519, prio: 120, lat: 67 } hitcount: 1 { pid: 2519, prio: 120, lat: 69 } hitcount: 1 { pid: 2521, prio: 19, lat: 1 } hitcount: 735 { pid: 2521, prio: 19, lat: 2 } hitcount: 8978 { pid: 2521, prio: 19, lat: 3 } hitcount: 4798 { pid: 2521, prio: 19, lat: 4 } hitcount: 716 { pid: 2521, prio: 19, lat: 5 } hitcount: 298 { pid: 2521, prio: 19, lat: 6 } hitcount: 136 { pid: 2521, prio: 19, lat: 7 } hitcount: 93 { pid: 2521, prio: 19, lat: 8 } hitcount: 51 { pid: 2521, prio: 19, lat: 9 } hitcount: 20 { pid: 2521, prio: 19, lat: 10 } hitcount: 18 { pid: 2521, prio: 19, lat: 11 } hitcount: 3 { pid: 2521, prio: 19, lat: 12 } hitcount: 1 { pid: 2521, prio: 19, lat: 13 } hitcount: 3 { pid: 2521, prio: 19, lat: 15 } hitcount: 1 { pid: 2521, prio: 19, lat: 17 } hitcount: 1 { pid: 2521, prio: 19, lat: 18 } hitcount: 1 { pid: 2521, prio: 19, lat: 20 } hitcount: 2 { pid: 2521, prio: 19, lat: 22 } hitcount: 1 { pid: 2521, prio: 19, lat: 25 } hitcount: 1 { pid: 2521, prio: 19, lat: 26 } hitcount: 1 { pid: 2522, prio: 19, lat: 1 } hitcount: 392 { pid: 2522, prio: 19, lat: 2 } hitcount: 5376 { pid: 2522, prio: 19, lat: 3 } hitcount: 3982 { pid: 2522, prio: 19, lat: 4 } hitcount: 500 { pid: 2522, prio: 19, lat: 5 } hitcount: 202 { pid: 2522, prio: 19, lat: 6 } hitcount: 67 { pid: 2522, prio: 19, lat: 7 } hitcount: 35 { pid: 2522, prio: 19, lat: 8 } hitcount: 12 { pid: 2522, prio: 19, lat: 9 } hitcount: 9 { pid: 2522, prio: 19, lat: 10 } hitcount: 4 { pid: 2522, prio: 19, lat: 11 } hitcount: 3 { pid: 2522, prio: 19, lat: 12 } hitcount: 1 { pid: 2522, prio: 19, lat: 13 } hitcount: 1 { pid: 2522, prio: 19, lat: 16 } hitcount: 1 { pid: 2522, prio: 19, lat: 18 } hitcount: 2 { pid: 2522, prio: 19, lat: 19 } hitcount: 1 { pid: 2522, prio: 19, lat: 21 } hitcount: 2 { pid: 2522, prio: 19, lat: 22 } hitcount: 1 { pid: 2522, prio: 19, lat: 23 } hitcount: 1 { pid: 2522, prio: 19, lat: 45 } hitcount: 1 { pid: 2522, prio: 19, lat: 82 } hitcount: 1 Totals: Hits: 28037 Entries: 65 Dropped: 0 Duplicates: 0 The above output uses the .usecs modifier to common_timestamp, so the latencies are reported in microseconds. The default, without the modifier, is nanoseconds, but that's too fine-grained to put directly into a histogram - for that however we can use the .log2 modifier on the 'lat' key. Otherwise the rest is the same: # echo 'wakeup_latency u64 lat; pid_t pid; int prio' >> \ /sys/kernel/debug/tracing/synthetic_events # echo 'hist:keys=pid:ts0=$common_timestamp if comm=="cyclictest"' >> \ /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger # echo 'hist:keys=next_pid:wakeup_lat=$common_timestamp-$ts0: \ onmatch(sched.sched_wakeup).wakeup_latency($wakeup_lat,next_pid,next_prio) \ if next_comm=="cyclictest"' >> \ /sys/kernel/debug/tracing/events/sched/sched_switch/trigger # echo 'hist:keys=pid,prio,lat.log2:sort=pid,lat' >> \ /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger # cat /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/hist # event histogram # # trigger info: hist:keys=pid,prio,lat.log2:vals=hitcount:sort=pid,lat.log2:size=2048 [active] # { pid: 2585, prio: 120, lat: ~ 2^10 } hitcount: 1 { pid: 2585, prio: 120, lat: ~ 2^11 } hitcount: 379 { pid: 2585, prio: 120, lat: ~ 2^12 } hitcount: 1008 { pid: 2585, prio: 120, lat: ~ 2^13 } hitcount: 42 { pid: 2585, prio: 120, lat: ~ 2^14 } hitcount: 18 { pid: 2585, prio: 120, lat: ~ 2^15 } hitcount: 3 { pid: 2585, prio: 120, lat: ~ 2^16 } hitcount: 1 { pid: 2586, prio: 19, lat: ~ 2^11 } hitcount: 4715 { pid: 2586, prio: 19, lat: ~ 2^12 } hitcount: 9161 { pid: 2586, prio: 19, lat: ~ 2^13 } hitcount: 632 { pid: 2586, prio: 19, lat: ~ 2^14 } hitcount: 47 { pid: 2586, prio: 19, lat: ~ 2^15 } hitcount: 3 { pid: 2586, prio: 19, lat: ~ 2^17 } hitcount: 1 { pid: 2587, prio: 19, lat: ~ 2^11 } hitcount: 3398 { pid: 2587, prio: 19, lat: ~ 2^12 } hitcount: 5762 { pid: 2587, prio: 19, lat: ~ 2^13 } hitcount: 505 { pid: 2587, prio: 19, lat: ~ 2^14 } hitcount: 58 { pid: 2587, prio: 19, lat: ~ 2^15 } hitcount: 3 { pid: 2587, prio: 19, lat: ~ 2^17 } hitcount: 1 Totals: Hits: 25738 Entries: 19 Dropped: 0 Duplicates: 0 ==== Example - wakeup latency with onmax() ==== This example is the same as the previous ones, but here we're additionally using the onmax() action to save some context (several fields of the sched_switch event) whenever the latency (wakeup_lat) exceeds the previous maximum. As with the similar functionality of the -RT latency_hist histograms, it's useful to be able to capture information about the previous process, which potentially could have contributed to the maximum latency that was saved. # echo 'wakeup_latency u64 lat; pid_t pid; int prio' >> \ /sys/kernel/debug/tracing/synthetic_events # echo 'hist:keys=pid:ts0=$common_timestamp.usecs if comm=="cyclictest"' >> \ /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger Here we add an onmax() action that saves some important fields of the sched_switch event along with the maximum, in addition to sending some of the same data to the synthetic event: # echo 'hist:keys=next_pid:wakeup_lat=$common_timestamp.usecs-$ts0: \ onmax($wakeup_lat).save(next_comm,prev_pid,prev_prio,prev_comm): \ onmatch(sched.sched_wakeup).wakeup_latency($wakeup_lat,next_pid,next_prio) \ if next_comm=="cyclictest"' >> \ /sys/kernel/debug/tracing/events/sched/sched_switch/trigger # echo 'hist:keys=pid,prio,lat:sort=pid,lat' >> \ /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger To see the maximums and associated data for each pid, cat the sched_switch event, as that's the event the onmax() action is associated with: # cat /sys/kernel/debug/tracing/events/sched/sched_switch/hist # event histogram # { next_pid: 6173 } hitcount: 199 max: 14 next_comm: cyclictest prev_pid: 0 \ prev_prio: 120 prev_comm: swapper/2 { next_pid: 6175 } hitcount: 1327 max: 15 next_comm: cyclictest prev_pid: 0 \ prev_prio: 120 prev_comm: swapper/2 { next_pid: 6174 } hitcount: 1985 max: 30 next_comm: cyclictest prev_pid: 0 \ prev_prio: 120 prev_comm: swapper/3 Totals: Hits: 17555 Entries: 3 Dropped: 0 Duplicates: 0 And, verifying, we can see that the max latencies captured above match the highest latencies for each thread in the wakeup_latency histogram: # cat /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/hist # event histogram # # trigger info: hist:keys=pid,prio,lat:vals=hitcount:sort=pid,lat:size=2048 [active] # { pid: 6173, prio: 120, lat: 1 } hitcount: 2 { pid: 6173, prio: 120, lat: 2 } hitcount: 82 { pid: 6173, prio: 120, lat: 3 } hitcount: 84 ... { pid: 6173, prio: 120, lat: 14 } hitcount: 1 { pid: 6174, prio: 19, lat: 1 } hitcount: 23 { pid: 6174, prio: 19, lat: 2 } hitcount: 749 ... { pid: 6174, prio: 19, lat: 30 } hitcount: 1 { pid: 6175, prio: 19, lat: 1 } hitcount: 20 { pid: 6175, prio: 19, lat: 2 } hitcount: 633 ... { pid: 6175, prio: 19, lat: 15 } hitcount: 1 Totals: Hits: 3511 Entries: 38 Dropped: 0 Duplicates: 0 ==== Example - combined wakeup and switchtime (wakeupswitch) latency ==== Finally, this example is quite a bit more involved, but that's because it implements 3 latencies, one which is a combination of the other two. This also, is something that the -RT latency_hist patchset does and which this patchset adds generic support for. The latency_hist patchset creates a few individual latency histograms but also combines them into larger overall combined histograms. For example, the time between when a thread is awakened and when it actually continues executing in userspace is something covered by a histogram, but it's also broken down into two sub-histograms, one covering the time between sched_wakeup and the time the thread is scheduled in (wakeup_latency as above), and the time between when the thread is scheduled in and the time it actually begins executing again (return from sys_nanosleep), covered by a separate switchtime_latency histogram. The below combines the wakeup_latency histogram from before, adds a new switchtime_latency histogram, and another, wakeupswitch_latency, that's a combination of the other two. There isn't anything really new here, other than that the use of the addition operator to add two latencies to produce the wakeupswitch_latency. First, we create the familiar wakeup_latency histogram: # echo 'wakeup_latency u64 lat; pid_t pid' >> \ /sys/kernel/debug/tracing/synthetic_events # echo 'hist:keys=pid:ts0=$common_timestamp.usecs \ if comm=="cyclictest"' >> \ /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger # echo 'hist:keys=next_pid:wakeup_lat=$common_timestamp.usecs-$ts0:\ onmatch(sched.sched_wakeup).wakeup_latency($wakeup_lat,next_pid) \ if next_comm=="cyclictest"' >> \ /sys/kernel/debug/tracing/events/sched/sched_switch/trigger Here we save the wakeup_latency lat value as wakeup_lat for use later in the combined latency: # echo 'hist:keys=pid,lat:wakeup_lat=lat:sort=pid,lat' \ >> /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger Next, we create the switchtime_latency histogram: # echo 'switchtime_latency u64 lat; pid_t pid' >> \ /sys/kernel/debug/tracing/synthetic_events Here we save the sched_switch next_pid field as 'pid'. This is so we can access the next_pid in the matching sys_exit_nanosleep event. # echo 'hist:keys=next_pid:pid=next_pid:ts0=$common_timestamp.usecs \ if next_comm=="cyclictest"' >> \ /sys/kernel/debug/tracing/events/sched/sched_switch/trigger # echo 'hist:keys=common_pid:switchtime_lat=$common_timestamp.usecs-$ts0: \ onmatch(sched.sched_switch).switchtime_latency($switchtime_lat,$pid)' \ >> /sys/kernel/debug/tracing/events/syscalls/sys_exit_nanosleep/trigger # echo 'hist:keys=pid,lat:sort=pid,lat' \ >> /sys/kernel/debug/tracing/events/synthetic/switchtime_latency/trigger Finally, we create the combined wakeupswitch_latency: # echo 'wakeupswitch_latency u64 lat; pid_t pid' >> \ /sys/kernel/debug/tracing/synthetic_events Here we calculate the combined latency using the saved $wakeup_lat variable from the wakeup_latency histogram and the lat value of the switchtime_latency, save it as ws_lat and then use it to generate the combined wakeupswitch latency: # echo 'hist:keys=pid,lat:sort=pid,lat:ws_lat=$wakeup_lat+lat: \ onmatch(synthetic.wakeup_latency).wakeupswitch_latency($ws_lat,pid)' \ >> /sys/kernel/debug/tracing/events/synthetic/switchtime_latency/trigger # echo 'hist:keys=pid,lat:sort=pid,lat' >> \ /sys/kernel/debug/tracing/events/synthetic/wakeupswitch_latency/trigger After running our cyclictest workload, we can now look at each histogram, starting with wakeup_latency: # cat /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/hist # event histogram # # trigger info: hist:keys=pid,lat:vals=hitcount:wakeup_lat=lat:sort=pid,lat:size=2048 [active] # { pid: 6852, lat: 1 } hitcount: 2 { pid: 6852, lat: 2 } hitcount: 88 { pid: 6852, lat: 3 } hitcount: 72 { pid: 6852, lat: 4 } hitcount: 19 { pid: 6852, lat: 5 } hitcount: 10 { pid: 6852, lat: 6 } hitcount: 1 { pid: 6852, lat: 7 } hitcount: 4 { pid: 6852, lat: 9 } hitcount: 2 { pid: 6852, lat: 10 } hitcount: 1 { pid: 6853, lat: 1 } hitcount: 1 { pid: 6853, lat: 2 } hitcount: 535 { pid: 6853, lat: 3 } hitcount: 1007 ... { pid: 6853, lat: 19 } hitcount: 1 { pid: 6853, lat: 20 } hitcount: 1 { pid: 6853, lat: 29 } hitcount: 1 { pid: 6854, lat: 1 } hitcount: 5 { pid: 6854, lat: 2 } hitcount: 552 { pid: 6854, lat: 3 } hitcount: 532 { pid: 6854, lat: 4 } hitcount: 135 { pid: 6854, lat: 5 } hitcount: 48 { pid: 6854, lat: 6 } hitcount: 18 { pid: 6854, lat: 7 } hitcount: 12 { pid: 6854, lat: 8 } hitcount: 5 ... { pid: 6854, lat: 29 } hitcount: 2 { pid: 6854, lat: 48 } hitcount: 1 Totals: Hits: 3501 Entries: 46 Dropped: 0 Duplicates: 0 Here's the switchtime histogram: # cat /sys/kernel/debug/tracing/events/synthetic/switchtime_latency/hist # event histogram # # trigger info: hist:keys=pid,lat:vals=hitcount:sort=pid,lat:size=2048 [active] # { pid: 6852, lat: 1 } hitcount: 1 { pid: 6852, lat: 2 } hitcount: 33 { pid: 6852, lat: 3 } hitcount: 73 { pid: 6852, lat: 4 } hitcount: 49 { pid: 6852, lat: 5 } hitcount: 28 { pid: 6852, lat: 6 } hitcount: 4 ... { pid: 6852, lat: 16 } hitcount: 1 { pid: 6853, lat: 1 } hitcount: 76 { pid: 6853, lat: 2 } hitcount: 1190 { pid: 6853, lat: 3 } hitcount: 475 { pid: 6853, lat: 4 } hitcount: 125 { pid: 6853, lat: 5 } hitcount: 40 { pid: 6853, lat: 6 } hitcount: 21 { pid: 6853, lat: 7 } hitcount: 13 { pid: 6853, lat: 8 } hitcount: 5 { pid: 6853, lat: 9 } hitcount: 11 ... { pid: 6853, lat: 20 } hitcount: 2 { pid: 6854, lat: 1 } hitcount: 13 { pid: 6854, lat: 2 } hitcount: 799 { pid: 6854, lat: 3 } hitcount: 332 { pid: 6854, lat: 4 } hitcount: 97 { pid: 6854, lat: 5 } hitcount: 29 { pid: 6854, lat: 6 } hitcount: 16 ... { pid: 6854, lat: 22 } hitcount: 1 { pid: 6854, lat: 26 } hitcount: 1 Totals: Hits: 3501 Entries: 48 Dropped: 0 Duplicates: 0 And here's the combined wakeupswitch latency histogram: # cat /sys/kernel/debug/tracing/events/synthetic/wakeupswitch_latency/hist # event histogram # # trigger info: hist:keys=pid,lat:vals=hitcount:sort=pid,lat:size=2048 [active] # { pid: 6852, lat: 4 } hitcount: 24 { pid: 6852, lat: 5 } hitcount: 47 { pid: 6852, lat: 6 } hitcount: 53 { pid: 6852, lat: 7 } hitcount: 29 ... { pid: 6852, lat: 25 } hitcount: 1 { pid: 6853, lat: 3 } hitcount: 5 { pid: 6853, lat: 4 } hitcount: 504 { pid: 6853, lat: 5 } hitcount: 753 { pid: 6853, lat: 6 } hitcount: 337 { pid: 6853, lat: 7 } hitcount: 149 { pid: 6853, lat: 8 } hitcount: 66 { pid: 6853, lat: 9 } hitcount: 45 { pid: 6853, lat: 10 } hitcount: 24 { pid: 6853, lat: 11 } hitcount: 26 { pid: 6853, lat: 12 } hitcount: 9 { pid: 6853, lat: 13 } hitcount: 13 { pid: 6853, lat: 14 } hitcount: 9 { pid: 6853, lat: 15 } hitcount: 3 { pid: 6853, lat: 17 } hitcount: 3 { pid: 6853, lat: 18 } hitcount: 5 { pid: 6853, lat: 19 } hitcount: 2 ... { pid: 6853, lat: 37 } hitcount: 1 { pid: 6853, lat: 38 } hitcount: 1 { pid: 6854, lat: 3 } hitcount: 7 { pid: 6854, lat: 4 } hitcount: 418 { pid: 6854, lat: 5 } hitcount: 493 { pid: 6854, lat: 6 } hitcount: 165 { pid: 6854, lat: 7 } hitcount: 81 { pid: 6854, lat: 8 } hitcount: 57 { pid: 6854, lat: 9 } hitcount: 27 { pid: 6854, lat: 10 } hitcount: 15 { pid: 6854, lat: 11 } hitcount: 13 { pid: 6854, lat: 12 } hitcount: 7 { pid: 6854, lat: 13 } hitcount: 10 { pid: 6854, lat: 14 } hitcount: 6 { pid: 6854, lat: 15 } hitcount: 5 { pid: 6854, lat: 16 } hitcount: 5 { pid: 6854, lat: 17 } hitcount: 2 { pid: 6854, lat: 18 } hitcount: 1 ... { pid: 6854, lat: 55 } hitcount: 1 Totals: Hits: 3501 Entries: 70 Dropped: 0 Duplicates: 0 Finally, just to show that synthetic events are indeed just like any other event as far as the event subsystem is concerned, we can enable the synthetic events and see the events appear in the trace buffer: # echo 1 > /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/enable # echo 1 > /sys/kernel/debug/tracing/events/synthetic/switchtime_latency/enable # echo 1 > /sys/kernel/debug/tracing/events/synthetic/wakeupswitch_latency/enable Below is a snippet of the contents of the trace file produced when the above histograms were generated: # cat /sys/kernel/debug/tracing/trace # tracer: nop # # entries-in-buffer/entries-written: 10503/10503 #P:4 # # _-----=> irqs-off # / _----=> need-resched # | / _---=> hardirq/softirq # || / _--=> preempt-depth # ||| / delay # TASK-PID CPU# |||| TIMESTAMP FUNCTION # | | | |||| | | -0 [001] d..2 23532.240146: wakeup_latency: lat=4, pid=6853 cyclictest-6853 [001] .... 23532.240153: switchtime_latency: lat=7, pid=6853 cyclictest-6853 [001] .... 23532.240157: wakeupswitch_latency: lat=11, pid=6853 gnome-terminal--2500 [001] d..2 23532.240672: wakeup_latency: lat=5, pid=6854 cyclictest-6854 [001] .... 23532.240676: switchtime_latency: lat=4, pid=6854 cyclictest-6854 [001] .... 23532.240677: wakeupswitch_latency: lat=9, pid=6854 gnome-terminal--2500 [001] d..2 23532.241169: wakeup_latency: lat=4, pid=6853 cyclictest-6853 [001] .... 23532.241172: switchtime_latency: lat=3, pid=6853 cyclictest-6853 [001] .... 23532.241174: wakeupswitch_latency: lat=7, pid=6853 -0 [001] d..2 23532.242189: wakeup_latency: lat=6, pid=6853 cyclictest-6853 [001] .... 23532.242195: switchtime_latency: lat=8, pid=6853 -0 [000] d..2 23532.242196: wakeup_latency: lat=12, pid=6854 cyclictest-6853 [001] .... 23532.240146: wakeupswitch_latency: lat=14, pid=6853 cyclictest-6854 [000] .... 23532.242196: switchtime_latency: lat=4, pid=6854 -0 [001] d..2 23532.240146: wakeup_latency: lat=2, pid=6853 cyclictest-6854 [000] .... 23532.242196: wakeupswitch_latency: lat=16, pid=6854 cyclictest-6853 [001] .... 23532.240146: switchtime_latency: lat=3, pid=6853 ... One quick note about usage - the introduction of variables and actions obviously makes it harder to determine the cause of a hist trigger command failure - 'Invalid argument' is no longer sufficient in many cases. For that reason, a new 'extended error' mechanism has been added to hist triggers, initially focused on variable and action-related errors, but something that could possibly expanded to other error conditions later. To make use of it, simply read the 'hist' file of the event that was the target of the command. In this example, we've entered the same command twice, resulting in an attempt to define the same variable (ts0) twice. After seeing the 'Invalid argument' error for the command, we read the same event's hist file and see a message to that effect at the bottom of the file: # echo 'hist:keys=pid:ts0=$common_timestamp.usecs if comm=="cyclictest"' >> \ /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger # echo 'hist:keys=pid:ts0=$common_timestamp.usecs if comm=="cyclictest"' >> \ /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger -su: echo: write error: Invalid argument # cat /sys/kernel/debug/tracing/events/sched/sched_wakeup/hist # event histogram # # Totals: Hits: 0 Entries: 0 Dropped: 0 Duplicates: 0 ERROR: Variable already defined: ts0 Last command: keys=pid:ts0=$common_timestamp.usecs if comm=="cyclictest" The following changes since commit 681bec0367c2606b6154060310a2ffa543175980: tracing: Rename update the enum_map file (2017-06-13 17:13:06 -0400) are available in the git repository at: https://github.com/tzanussi/linux-trace-inter-event.git tzanussi/inter-event-v01 https://github.com/tzanussi/linux-trace-inter-event/tree/tzanussi/inter-event-v01 Tom Zanussi (32): tracing: Add hist_field_name() accessor tracing: Reimplement log2 ring-buffer: Add interface for setting absolute time stamps ring-buffer: Redefine the unimplemented RINGBUF_TIME_TIME_STAMP tracing: Give event triggers access to ring_buffer_event tracing: Add ring buffer event param to hist field functions tracing: Increase tracing map KEYS_MAX size tracing: Break out hist trigger assignment parsing tracing: Make traceprobe parsing code reusable tracing: Add NO_DISCARD event file flag tracing: Add post-trigger flag to hist trigger command tracing: Add hist trigger timestamp support tracing: Add per-element variable support to tracing_map tracing: Add hist_data member to hist_field tracing: Add usecs modifier for hist trigger timestamps tracing: Add variable support to hist triggers tracing: Account for variables in named trigger compatibility tracing: Add simple expression support to hist triggers tracing: Add variable reference handling to hist triggers tracing: Add support for dynamic tracepoints tracing: Add hist trigger action hook tracing: Add support for 'synthetic' events tracing: Add 'onmatch' hist trigger action support tracing: Add 'onmax' hist trigger action support tracing: Allow whitespace to surround hist trigger filter tracing: Make duplicate count from tracing_map available tracing: Add cpu field for hist triggers tracing: Add hist trigger support for variable reference aliases tracing: Add 'last error' error facility for hist triggers tracing: Add inter-event hist trigger Documentation tracing: Make tracing_set_clock() non-static tracing: Add a clock attribute for hist triggers Documentation/trace/events.txt | 422 ++++ include/linux/ring_buffer.h | 14 +- include/linux/trace_events.h | 17 +- include/linux/tracepoint.h | 11 +- kernel/trace/ring_buffer.c | 118 +- kernel/trace/trace.c | 121 +- kernel/trace/trace.h | 36 +- kernel/trace/trace_events.c | 4 +- kernel/trace/trace_events_hist.c | 4107 ++++++++++++++++++++++++++++++++--- kernel/trace/trace_events_trigger.c | 69 +- kernel/trace/trace_kprobe.c | 18 +- kernel/trace/trace_probe.c | 86 - kernel/trace/trace_probe.h | 7 - kernel/trace/trace_uprobe.c | 2 +- kernel/trace/tracing_map.c | 125 +- kernel/trace/tracing_map.h | 16 +- kernel/tracepoint.c | 42 +- 17 files changed, 4684 insertions(+), 531 deletions(-) -- 1.9.3