On 2024-10-26 03:13, Steven Rostedt wrote:
On Fri, 25 Oct 2024 15:38:48 -0400
Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote:
I'm curious if it might be better to add some field to struct
tracepoint like "sleepable" rather than adding a special case here
based on the name? Of course, if it's only ever going to be these
two cases then maybe adding a new field doesn't make sense.
I know Steven is reluctant to bloat the tracepoint struct because there
are lots of tracepoint instances (thousands). So for now I thought that
just comparing the name would be a good start.
You are correct. I really trying to keep the footprint of
tracepoints/events down.
We can eventually go a different route as well: introduce a section just
to put the syscall tracepoints, and compare the struct tracepoint
pointers to the section begin/end range. But it's rather complex
for what should remain a simple fix.
A separate section could work.
I have another approach to suggest: it shrinks the
size of struct tracepoint from 80 bytes down to 72 bytes
on x86-64, we don't have to do any section/linker
script trickery, and it's extensible for future flags:
struct static_key {
int enabled;
void *p;
};
struct static_key_false {
struct static_key key;
};
struct static_call_key {
void *func;
void *p;
};
struct tracepoint {
const char *name; /* Tracepoint name */
struct static_key_false key;
struct static_call_key *static_call_key;
void *static_call_tramp;
void *iterator;
void *probestub;
void *funcs;
/* Flags. */
unsigned int regfunc:1,
syscall:1;
};
struct tracepoint_regfunc {
struct tracepoint tp;
int (*regfunc)(void);
void (*unregfunc)(void);
};
Basically, a tracepoint with regfunc would define a
struct tracepoint_regfunc rather than a struct tracepoint.
So we remove both regfunc and unregfunc NULL pointers in
the common case, which gives us plenty of room for flags.
When we want to access the regfunc/unregfunc from
a struct tracepoint, we check the regfunc flag, and
if set, we can use container_of() to get the struct
tracepoint_regfunc.
Thoughts ?
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
