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Reduce ftrace overhead to 280ns

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This commit is contained in:
Justine Tunney 2022-05-20 04:46:42 -07:00
parent 4245da19e2
commit c8a2f04058
2 changed files with 33 additions and 17 deletions
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40
libc/runtime/ftracer.c
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@ -18,10 +18,12 @@
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/calls/calls.h"
#include "libc/fmt/itoa.h"
#include "libc/intrin/cmpxchg.h"
#include "libc/intrin/kprintf.h"
#include "libc/intrin/lockcmpxchgp.h"
#include "libc/macros.internal.h"
#include "libc/nexgen32e/stackframe.h"
#include "libc/nexgen32e/threaded.h"
#include "libc/runtime/stack.h"
#include "libc/runtime/symbols.internal.h"
@ -69,21 +71,29 @@ static privileged inline void ReleaseFtraceLock(void) {
static privileged inline bool AcquireFtraceLock(void) {
int me, owner, tries;
for (tries = 0, me = gettid();;) {
owner = 0;
if (_lockcmpxchgp(&ftrace_lock, &owner, me)) {
return true;
}
if (owner == me) {
// we ignore re-entry into ftrace. while the code and build config
// is written to make re-entry highly unlikely, it's impossible to
// guarantee. there's also the possibility of asynchronous signals
return false;
}
if (++tries & 7) {
__builtin_ia32_pause();
} else {
sched_yield();
if (!__threaded) {
return _cmpxchg(&ftrace_lock, 0, -1);
} else {
for (tries = 0, me = gettid();;) {
owner = 0;
if (_lockcmpxchgp(&ftrace_lock, &owner, me)) {
return true;
}
if (owner == -1) {
// avoid things getting weird after first clone() call transition
return false;
}
if (owner == me) {
// we ignore re-entry into ftrace. while the code and build config
// is written to make re-entry highly unlikely, it's impossible to
// guarantee. there's also the possibility of asynchronous signals
return false;
}
if (++tries & 7) {
__builtin_ia32_pause();
} else {
sched_yield();
}
}
}
}