Messages in this thread | | | Date | Wed, 09 Sep 2009 10:18:40 +0800 | From | Li Zefan <> | Subject | Re: [PATCH 4/6] perf_counter: Add PERF_COUNTER_IOC_SET_FILTER ioctl |
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>>>> Hrm,.. not at all sure about this.. what are the ABI implications? >>> I think the ABI should be fine if it's always a sub-set of C syntax. >>> That would be C expressions initially. Hm? >> Right, so I've no clue what filter expressions look like, and the >> changelog doesn't help us at all. It doesn't mention its a well >> considered decision to henceforth freeze the expression syntax. >> >> Of course, since filters so far only work with tracepoint things, and >> since you can only come by tracepoint things through debugfs, and since >> anything debugfs is basically a free-for-all ABI-less world, we might be >> good, but then this is a very ill-defined ioctl() indeed. >> >> So please, consider this well -- there might not be a second chance. >> > > I've been meaning to write up something about the event filters - here's > a first stab that hopefully helps explain them... >
Great!
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Could you add your SOB and send it to Ingo?
Some nitpicks below:
> Tom > > diff --git a/Documentation/trace/events.txt b/Documentation/trace/events.txt > index 2bcc8d4..50fe510 100644 > --- a/Documentation/trace/events.txt > +++ b/Documentation/trace/events.txt > @@ -97,3 +97,160 @@ The format of this boot option is the same as described in section 2.1. > > See The example provided in samples/trace_events > > +4. Event formats > +================ > + > +Each trace event has a 'format' file associated with it that contains > +a description of each field in a logged event. This information can > +be used to parse the binary trace stream, and is also the place to > +find the field names that can be used in event filters (see section 5 > +below). > + > +It also displays the format string that will be used to print the > +event in text mode, along with the event name and ID used for > +profiling. > + > +Every event has a set of 'common' fields associated with it; these are > +the fields prefixed with 'common_'. The other fields vary between > +events and correspond to the fields defined in the TRACE_EVENT > +definition for that event. > + > +Here's the information displayed for the 'sched_wakeup' event: > + > +# cat /debug/tracing/events/sched/sched_wakeup/format > + > +name: sched_wakeup > +ID: 60 > +format: > + field:unsigned short common_type; offset:0; size:2; > + field:unsigned char common_flags; offset:2; size:1; > + field:unsigned char common_preempt_count; offset:3; size:1; > + field:int common_pid; offset:4; size:4; > + field:int common_tgid; offset:8; size:4; > + > + field:char comm[TASK_COMM_LEN]; offset:12; size:16; > + field:pid_t pid; offset:28; size:4; > + field:int prio; offset:32; size:4; > + field:int success; offset:36; size:4; > + field:int cpu; offset:40; size:4; > + > +print fmt: "task %s:%d [%d] success=%d [%03d]", REC->comm, REC->pid, REC->prio, REC->success, REC->cpu > + > +5. Event filtering > +================== > +
How about adding titles 5.1, 5.2, 5.3?
5.1 expression syntax
5.2 set a filter
5.3 clear a filter
5.4 subsystem filter
> +Trace events can be filtered in the kernel by associating boolean > +'filter expressions' with them. As soon as an event is logged into > +the trace buffer, its fields are checked against the filter expression > +associated with that event type. An event with field values that > +'match' the filter will appear in the trace output, and an event whose > +values don't match will be discarded. An event with no filter > +associated with it matches everything, which is the default when no > +filter has been set for an event. > + > +A filter expression consists of one or more 'predicates' that can be > +combined using the logical operators '&&' and '||'. A predicate is > +simply a clause that compares the value of a field contained within a > +logged event with a constant value and returns either 0 or 1 depending > +on whether the field value matched (1) or didn't match (0): > + > + field-name relational-operator value > + > +Parentheses can be used to provide arbitrary logical groupings and > +double-quotes can be used to prevent the shell from interpreting > +operators as shell metacharacters. > + > +The field-names available for use in filters can be found in the > +'format' files for trace events (see section 4 above). > + > +The relational-operators depend on the type of the field being tested: > + > +The operators available for numeric fields are: > + > +==, !=, <, <=, >, >= > + > +And for string fields they are: > + > +==, != > + > +Currently, only exact string matches are supported. > + > +Currently, the maximum number of predicates in a filter is set at 16. > + > +A filter for an individual event is set by writing a filter expression > +to the 'filter' file for the given event. > + > +For example: > + > +# cd /debug/tracing/events/sched/sched_wakeup > +# echo "common_preempt_count > 4" > filter > + > +A slightly more involved example: > + > +# cd /debug/tracing/events/sched/sched_signal_send > +# echo "((sig >= 10 && sig < 15) || sig == 17) && comm != bash" > filter > + > +If there was an error in the expression, you'll get an 'Invalid > +argument' error when setting it, and the erroneous string along with > +an error message can be seen by looking at the filter e.g.: > + > +# cd /debug/tracing/events/sched/sched_signal_send > +# echo "((sig >= 10 && sig < 15) || dsig == 17) && comm != bash" > filter > +-bash: echo: write error: Invalid argument > +# cat filter > +((sig >= 10 && sig < 15) || dsig == 17) && comm != bash > +^ > +parse_error: Field not found > + > +Currently the caret for an error always appears at the beginning of > +the filter string; the error message should be still be useful though
s/should be still be/should still be
> +even without more accurate position info. > + > +To clear a filter, write a '0' to the filter file. > + > +For convenience, filters for every event in a subsystem can be set or > +cleared as a group by writing a filter expression into the filter file > +at the root of the subsytem. Note, however, that if a filter for any > +event within the subsystem lacks a field specified in the subsystem > +filter, or if the filter can't be applied for any other reason, the > +filter for that event will retain its previous setting. This can > +result in an unintended mixture of filters which could lead to > +confusing (to the user who might think different filters are in > +effect) trace output. Only filters that reference just the common > +fields can be guaranteed to propagate successfully to all events. > + > +To clear the filters for all events in a subsystem, write a '0' to the > +subsystem's filter file. > + > +Here are a few subsystem filter examples that also illustrate the > +above points: > + > +Clear the filters on all events in the sched subsytem: > + > +# cd /sys/kernel/debug/tracing/events/sched > +# echo 0 > filter > +# cat sched_switch/filter > +none > +# cat sched_switch/filter > +none > + > +Set a filter using only common fields for all events in the sched > +subsytem (all events end up with the same filter): > + > +# cd /sys/kernel/debug/tracing/events/sched > +# echo common_pid == 0 > filter > +# cat sched_switch/filter > +common_pid == 0 > +# cat sched_wakeup/filter > +common_pid == 0 > + > +Attempt to set a filter using a non-common field for all events in the > +sched subsytem (all events but those that have a prev_pid field retain > +their old filters): > + > +# cd /sys/kernel/debug/tracing/events/sched > +# echo prev_pid == 0 > filter > +# cat sched_switch/filter > +prev_pid == 0 > +# cat sched_wakeup/filter > +common_pid == 0 >
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