Hello,
In the past I used to use "printf" for observability in the newly developed
kernel components, and now I would like to switch to dtrace probes, as this
appears to be a cleaner approach.
I have tried adding/tracing new probes today, and I am having trouble tracing
the new Dtrace probes that I have added to the kernel.
I have added the following probes to ts.c (the time-sharing scheduling class
module that I am modifying):
DTRACE_SCHED3(schedctl__intxn, kthread_t *, t, txnid_t,
schedctl_get_txnid(t), txnver_t, schedctl_get_txnver(t));
DTRACE_SCHED(schedctl__notxn);
I have compiled the TS module and installed it on the system. I have tested
that my workload actually executed the code around these Dtrace probes by
inserting printfs right after the probes and by making sure that the output of
those printfs appear on the system console. So I assume that those probes must
have been triggered.
Then I have written the following dtrace script dtrace.d:
--- begin script ---
#!/usr/sbin/dtrace -s
sched:::schedctl-intxn
/execname == "settxnid"/
{
printf("Txn_id = %ld, txn_ver = %ld\n", arg1, arg2);
printf("In txn\n");
}
sched:::schedctl-notxn
/execname == "settxnid"/
{
}
--- end script ---
Then I ran dtrace as follows:
sudo ./dtrace.d
#!/usr/sbin/dtrace -s
dtrace script './dtrace.d' matched 2 probes
(So my new probes were recognized)
Then I ran the workload that would trigger those probes, but the script did not
print anything. Yet, the output of my printfs (located just after those DTRACE
statements in the code) did appear on the console, indicating that the probes
were in fact triggered.
So it appears to me that the probes are triggered, but their output is not
displayed. Any ideas what I am doing wrong?
Thank you!
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