https://github.com/apache/trafficserver/pull/7452
This PR changes TS API. It introduces this new type:
typedef struct TSFDbgCtl_s {
char volatile on; // Flag
char const *tag;
} TSFDbgCtl;
And this function:
tsapi TSFDbgCtl const *TSFDbgCtlCreate(char const *tag);
And this new printf-like macro:
#define TSFDbg(ctlp, ...)
Where the first parameter is a pointer returned by TSFDbgCtlCreate(), the
second a printf format string, and the rest the parameters referenced the
format string.
In my performance test, enabling the new type of debug output resulted in a
10% reduction in requests per second handled, versus a 95% reduction due to
enabling the old type of debug output. (See
https://gist.github.com/ywkaras/4b0386341a4a6ce0afacaf46dcce79d6 )
If we decide to proceed with this, I think we have two options:
1. Proceed with the approach where enabling low-overhead debug output
will only work for Debug()/TSFDbg calls that use a DbgCtl/TSDbgCtl instance
rather than a simple tag string. This would include adding doc changes and
Au testing.
2. Switch to an approach similar to what I used for testing. Where
Debug() calls and is_debug_tag_set() will (each) generate a hidden instance
of DbgCtl. I think I can also make TSDebug() generate a hidden pointer to
TSFDbgCt.
