Rename "tsc" to "timestamp"
[lttng-ust.git] / doc / man / tracef-tracelog-limitations.txt
1 // SPDX-FileCopyrightText: 2016 Philippe Proulx <pproulx@efficios.com>
2 // SPDX-License-Identifier: CC-BY-4.0
3 //
4 :macro-name: lttng_ust_{macro-suffix}
5 :vmacro-name: lttng_ust_v{macro-suffix}
6
7 The +{macro-name}()+ and +{vmacro-name}()+ utility macros were
8 developed to make user space tracing super simple, albeit with notable
9 disadvantages compared to custom, full-fledged tracepoint providers:
10
11 * All generated events have the same provider/event names.
12 * There's no static type checking.
13 * The only event field with user data you actually get, named `msg`,
14 is a string potentially containing the values you passed to the
15 macro using your own format. This also means that you cannot use
16 filtering using a custom expression at run time because there are no
17 isolated fields.
18 * Since +{macro-name}()+ and +{vmacro-name}()+ use C standard
19 library's man:vasprintf(3) function in the background to format the
20 strings at run time, their expected performance is lower than using
21 custom tracepoint providers with typed fields, which do not require
22 a conversion to a string.
23 * Generally, a string containing the textual representation of the
24 user data fields is not as compact as binary fields in the resulting
25 trace.
26
27 Thus, +{macro-name}()+/+{vmacro-name}()+ are useful for quick
28 prototyping and debugging, but should not be considered for any
29 permanent/serious application instrumentation.
30
31 +{vmacro-name}()+ does not have a `STAP_PROBEV()` call, because
32 `STAP_PROBEV()` does not support `va_list`. If you need it, you should
33 emit this call yourself.
34
35 See man:lttng-ust(3) to learn more about custom tracepoint providers.
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