Am Mi., 19. Mai 2021 um 20:52 Uhr schrieb Mathieu Desnoyers <mathieu.desnoy...@efficios.com>: > > ----- On May 19, 2021, at 8:11 AM, lttng-dev lttng-dev@lists.lttng.org wrote: > > > Hello, > > > > Several context fields will cause a syscall atleast the first time a > > tracepoint is > > recorded. For example all of the following: > > > > `lttng add-context -c chan --userspace --type=vpid --type=vtid > > --type=procname` > > > > Each of them seems cached in TLS however, and most should never change > > after startup. > > > > As I am using Lttng over Xenomai, syscalls are strictly forbidden, I > > would like to have some function that prepares all data, which I can > > call on each thread before it switches to realtime work. > > > > Kinda similar to urcu_bp_register_thread, I'd like to have some > > `lttng_ust_warmup_thread` function that fetches the context values > > that can be cached. (urcu_bp_register_thread should be called there > > aswell) > > I considered just doing a tracepoint, but AFAIK the channel can be > > changed/configured after the process is running. So this is not robust > > enough. > > The new lttng_ust_init_thread() API in lttng-ust 2.13 would be the right > place to do this I think: > > /* > * Initialize this thread's LTTng-UST data structures. There is > * typically no need to call this, because LTTng-UST initializes its > * per-thread data structures lazily, but it should be called explicitly > * upon creation of each thread before signal handlers nesting over > * those threads use LTTng-UST tracepoints. > */ > > It would make sense that this new initialization helper also initializes > all contexts which cache the result of a system call. Considering that > contexts can be used from the filter and capture bytecode interpreter, as > well as contexts added to channels, I think we'd need to simply initialize > them all.
Yeah, just figured that it doesnt help at all if I do a tracepoint, as it might just be disabled ;) lttng_ust_init_thread() sounds right for that, maybe add one or 2 arguments for stuff you want initialized / dont want initialized over the default. I take that the downside of eager initialization is potentially wasted resources (now ignoring any one-time runtime cost). Norbert _______________________________________________ lttng-dev mailing list lttng-dev@lists.lttng.org https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
