[lttng-dev] lttng

[Thibault, Daniel]

> Message: 1
> Date: Fri, 3 May 2013 10:42:22 -0400
>
> There are now two tracing modes implemented in lttng-ust (user-space tracer), each with their own advantages (+)/disadvantages(-):
>
> 1) per-pid buffer tracing,
> [...]
> 2) per-uid (shared) buffer tracing, (buffers shared across applications
>    with same user ID)
>   + less memory overhead, less runtime overhead for short-lived
>     processes,
>   - if a process dies between reserve and commit, it creates a whole in
>     the subbuffer. This whole will be detected only when the producer
>     will fill up the buffer and find the unbalanced reserved/commit
>     counter the next time it reaches this sub-buffer. Until the buffer
>     the unbalanced reserve/commit count is observed by a producer,
>     the consumer is unable to read the buffer futher than the packet
>     containing the "whole". When the producer rebalances this packet's
>     reserve/commit count, it will be counted as a "discarded" packet,
>     and we lose all data within the packet that contains the whole.

   whole ⇒ hole

   This changes the meaning completely.   :-)

Daniel U. Thibault
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