On Dec 4, 2007, at 3:18 AM, perfoptimization-dev-
email@hidden wrote:
Hi,
I want to trace the context switch event and log the id of the
thread which is ending/starting the execution. I was required to use
Dtrace to log the events so I read the manual doc (http://docs.sun.com/app/docs/doc/817-6223
). The doc said I can use sched provider to fire various probes such
as off-cpu and on-cpu. However, on Leopard (build 9A581) I cannot
find sched provider.(I used 'sudo dtrace -l' but cannot find sched
provider in the output.)
Correct. That deficiency in Leopard is covered by the venerable:
<rdar://problem/4487709> dtrace needs a scheduler provider
Therefore, I tried some other probes. I assumed that all context
switch events are caused by the kernel API thread_switch. If my
assumption is correct, I can use the probe
fbt:mach_kernel:thread_switch:entry to trace the context switch
event. I would like to check whether my assumption is correct or not.
Incorrect. The mach_kernel:thread_switch: probe is placed on the mach
trap that services explicit *user* requests to schedule among its
threads. Context switch occurs at a deeper level in the kernel.
Are there any other options I can take?
I use the following in an internal tool. It is unsupported, subject to
breakage at any kernel update, YMMV etc. --
self->swout = (uint32_t)curthread;
/*
* thread_timer_event() is always called with "&thread-
>system_timer" passed as new_timer.
* This allows for the nasty hack below where the value of
"thread" is recovered by
* subtracting the offset of the system_timer member.
*/
/* uint64_t tstamp sits in arg0:arg1. timer_t new_timer is arg2! */
self->swin = ((uint32_t)arg2 - offsetof(struct thread,
system_timer));
}
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