Hi,
I am fairly new to DTrace, and wanted to ask something regarding
synchronization objects.
I have a multithreaded C++ program in which I use semaphores (POSIX version)
for synchronization. I was interested in using DTrace to figure out the
total time for which each thread in my application sleeps, blocked on a
semaphore, i.e., as a result of sem_wait() call. In order to measure this, I
wrote a script with sched:::sleep and sched:wakeup probes enabled, as shown
below:
sched:::sleep
/execname == "myexecname"/
{
ustack();
bedtime[curlwpsinfo->pr_addr,curlwpsinfo->pr_stype] = walltimestamp;
}
sched:::wakeup
/bedtime[args[0]->pr_addr,args[0]->pr_stype]/
{
@sleeptime[execname,args[0]->pr_lwpid,args[0]->pr_addr,args[0]->pr_stype] =
sum(walltimestamp - bedtime[args[0]->pr_addr,args[0]->pr_stype]);
bedtime[args[0]->pr_addr,args[0]->pr_stype] = 0;
}
On running my program along with this script, I could see (because of
ustack()) that the program is following the expected path to sem_wait() call
and then enters cv_block:sleep. The aggregation output showed that the
threads in my program are sleeping on pr_stype = 3 (translates to SOBJ_CV
according to the file sobject.h). However, I was expecting to see the
threads sleeping on pr_stype = 5 (SOBJ_USER) as a result of sem_wait()
calls, because the description of pr_stype field in struct lwpsinfo_t says
that (and I quote from chapter 25 of the DTrace guide):
The pr_stype field is set when the thread is sleeping on a synchronization
object.
The possible values for the pr_stype field are:
SOBJ_MUTEX
SOBJ_RWLOCK
...
SOBJ_USER : A user-level synchronization object. All blocking on user-level
synchronization objects is handled with SOBJ_USER synchronization
objects. User-level synchronization objects include those created with
mutex_init(3), sema_init(3C), rwlock_init(3C),
cond_init(3C) and their POSIX equivalents.
...
SOBJ_SHUTTLE
I was not surprised that the threads are sleeping on other synchronization
objects as well, but no account of SOBJ_USER was a little surprising.
Although I can see from ustack() that sem_wait() ultimately leads to
cv_block:sleep, was I wrong in expecting to see pr_stype = SOBJ_USER in the
output? Can someone please explain what is going on?
In case this is not the correct forum for such questions, please direct me
to a suitable forum. Thank you for your time.
Regards,
Priya
_______________________________________________
dtrace-discuss mailing list
[email protected]
