Author: mjg
Date: Tue May 22 08:27:33 2018
New Revision: 334026
URL: https://svnweb.freebsd.org/changeset/base/334026
Log:
Reduce sdt-related branch-fest in mi_switch.
The code was evaluating flags before resorting to checking if dtrace is
enabled. This was inducing forward jumps in the common case.
Modified:
head/sys/kern/kern_synch.c
Modified: head/sys/kern/kern_synch.c
==============================================================================
--- head/sys/kern/kern_synch.c Tue May 22 07:56:58 2018 (r334025)
+++ head/sys/kern/kern_synch.c Tue May 22 08:27:33 2018 (r334026)
@@ -431,8 +431,9 @@ mi_switch(int flags, struct thread *newtd)
CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)",
td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name);
#ifdef KDTRACE_HOOKS
- if ((flags & SW_PREEMPT) != 0 || ((flags & SW_INVOL) != 0 &&
- (flags & SW_TYPE_MASK) == SWT_NEEDRESCHED))
+ if (__predict_false(sdt_probes_enabled) &&
+ ((flags & SW_PREEMPT) != 0 || ((flags & SW_INVOL) != 0 &&
+ (flags & SW_TYPE_MASK) == SWT_NEEDRESCHED)))
SDT_PROBE0(sched, , , preempt);
#endif
sched_switch(td, newtd, flags);
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