[PATCH 1/3] io_submit.stp: fix array membership test

[Jeff Moyer <jmoyer at redhat dot com>]

io_submit.stp keeps track of threads which are currently executing
in the io_submit system call like so:

probe syscall.io_submit {
          in_iosubmit[tid()] = 1
}

probe syscall.io_submit.return {
          /* this assumes a given proc will do lots of io_submit calls, and
           * so doesn't do the more expensive "delete in_iosubmit[p]".  If
           * there are lots of procs doing small number of io_submit calls,
           * the hash may grow pretty big, so using delete may be better
           */
          in_iosubmit[tid()] = 0
}

However, the test to see if a thread is currently executing in io_submit
is performed using the membership operator 'in':

  if (tid() in in_iosubmit)

This is obviously wrong.  We can do one of two things:
1) change the test to if (in_iosubmit[tid()] == 1) or
2) just perform the delete in the return probe

While I agree that we typically have a small number of threads performing
io_submit, I don't believe there is substance to the performance claims
for the delete operator.  So, I've opted for solution 2.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
---
 testsuite/systemtap.examples/io/io_submit.stp | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/testsuite/systemtap.examples/io/io_submit.stp b/testsuite/systemtap.examples/io/io_submit.stp
index 74ab639..c5edd66 100755
--- a/testsuite/systemtap.examples/io/io_submit.stp
+++ b/testsuite/systemtap.examples/io/io_submit.stp
@@ -28,12 +28,7 @@ probe syscall.io_submit {
  * when we return from sys_io_submit, record that we're no longer there
  */
 probe syscall.io_submit.return {
-  /* this assumes a given proc will do lots of io_submit calls, and
-   * so doesn't do the more expensive "delete in_iosubmit[p]".  If
-   * there are lots of procs doing small number of io_submit calls,
-   * the hash may grow pretty big, so using delete may be better
-   */
-  in_iosubmit[tid()] = 0
+  delete in_iosubmit[tid()]
 }
 
 /*
-- 
2.8.2.335.g4bb51ae