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    SubjectRe: [PATCH v5 24/37] tracing: Add support for 'synthetic' events
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    Hi Namhyung,

    On Tue, 2017-11-14 at 10:21 +0900, Namhyung Kim wrote:
    > Hi Tom,
    >
    > On Thu, Nov 09, 2017 at 02:33:55PM -0600, Tom Zanussi wrote:
    > > Synthetic events are user-defined events generated from hist trigger
    > > variables saved from one or more other events.
    > >
    > > To define a synthetic event, the user writes a simple specification
    > > consisting of the name of the new event along with one or more
    > > variables and their type(s), to the tracing/synthetic_events file.
    > >
    > > For instance, the following creates a new event named 'wakeup_latency'
    > > with 3 fields: lat, pid, and prio:
    > >
    > > # echo 'wakeup_latency u64 lat; pid_t pid; int prio' >> \
    > > /sys/kernel/debug/tracing/synthetic_events
    > >
    > > Reading the tracing/synthetic_events file lists all the
    > > currently-defined synthetic events, in this case the event we defined
    > > above:
    > >
    > > # cat /sys/kernel/debug/tracing/synthetic_events
    > > wakeup_latency u64 lat; pid_t pid; int prio
    > >
    > > At this point, the synthetic event is ready to use, and a histogram
    > > can be defined using it:
    > >
    > > # echo 'hist:keys=pid,prio,lat.log2:sort=pid,lat' >> \
    > > /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
    > >
    > > The new event is created under the tracing/events/synthetic/ directory
    > > and looks and behaves just like any other event:
    > >
    > > # ls /sys/kernel/debug/tracing/events/synthetic/wakeup_latency
    > > enable filter format hist id trigger
    > >
    > > Although a histogram can be defined for it, nothing will happen until
    > > an action tracing that event via the trace_synth() function occurs.
    > > The trace_synth() function is very similar to all the other trace_*
    > > invocations spread throughout the kernel, except in this case the
    > > trace_ function and its corresponding tracepoint isn't statically
    > > generated but defined by the user at run-time.
    > >
    > > How this can be automatically hooked up via a hist trigger 'action' is
    > > discussed in a subsequent patch.
    > >
    > > Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
    > > ---
    >
    > [SNIP]
    > > +static const char *synth_field_fmt(char *type)
    > > +{
    > > + const char *fmt = "%llu";
    > > +
    > > + if (strcmp(type, "s64") == 0)
    > > + fmt = "%lld";
    > > + else if (strcmp(type, "u64") == 0)
    > > + fmt = "%llu";
    > > + else if (strcmp(type, "s32") == 0)
    > > + fmt = "%d";
    > > + else if (strcmp(type, "u32") == 0)
    > > + fmt = "%u";
    > > + else if (strcmp(type, "s16") == 0)
    > > + fmt = "%d";
    > > + else if (strcmp(type, "u16") == 0)
    > > + fmt = "%u";
    > > + else if (strcmp(type, "s8") == 0)
    > > + fmt = "%d";
    > > + else if (strcmp(type, "u8") == 0)
    > > + fmt = "%u";
    > > + else if (strcmp(type, "char") == 0)
    > > + fmt = "%d";
    > > + else if (strcmp(type, "unsigned char") == 0)
    > > + fmt = "%u";
    > > + else if (strcmp(type, "int") == 0)
    > > + fmt = "%d";
    > > + else if (strcmp(type, "unsigned int") == 0)
    > > + fmt = "%u";
    > > + else if (strcmp(type, "long") == 0)
    > > + fmt = "%ld";
    > > + else if (strcmp(type, "unsigned long") == 0)
    > > + fmt = "%lu";
    > > + else if (strcmp(type, "pid_t") == 0)
    > > + fmt = "%d";
    > > + else if (strstr(type, "[") == 0)
    > > + fmt = "%s";
    >
    > Is it for string? You may want to check it with '!='..
    >

    It is for a string, will change (and to strchr).

    Thanks,

    Tom

    > Thanks,
    > Namhyung
    >
    >
    > > +
    > > + return fmt;
    > > +}


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