On 2019-12-12 15:10, Cornelia Huck wrote:
On Thu, 12 Dec 2019 15:01:07 +0100
Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:
On 2019-12-12 13:01, Cornelia Huck wrote:
On Wed, 11 Dec 2019 16:46:08 +0100
Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:
A second step when testing the channel subsystem is to prepare a channel
for use.
This includes:
- Get the current SubCHannel Information Block (SCHIB) using STSCH
- Update it in memory to set the ENABLE bit
- Tell the CSS that the SCHIB has been modified using MSCH
- Get the SCHIB from the CSS again to verify that the subchannel is
enabled.
This tests the success of the MSCH instruction by enabling a channel.
Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
---
s390x/css.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 65 insertions(+)
+ /* Read the SCHIB for this subchannel */
+ cc = stsch(test_device_sid, &schib);
+ if (cc) {
+ report(0, "stsch cc=%d", cc);
+ return;
+ }
+
+ /* Update the SCHIB to enable the channel */
+ pmcw->flags |= PMCW_ENABLE;
+
+ /* Tell the CSS we want to modify the subchannel */
+ cc = msch(test_device_sid, &schib);
+ if (cc) {
+ /*
+ * If the subchannel is status pending or
+ * if a function is in progress,
+ * we consider both cases as errors.
+ */
+ report(0, "msch cc=%d", cc);
+ return;
+ }
+
+ /*
+ * Read the SCHIB again to verify the enablement
+ * insert a little delay and try 5 times.
+ */
+ do {
+ cc = stsch(test_device_sid, &schib);
+ if (cc) {
+ report(0, "stsch cc=%d", cc);
+ return;
+ }
+ delay(10);
That's just a short delay to avoid a busy loop, right? msch should be
immediate,
Thought you told to me that it may not be immediate in zVM did I
misunderstand?
Maybe I have been confusing... what I'm referring to is this
programming note for msch:
"It is recommended that the program inspect the
contents of the subchannel by subsequently
issuing STORE SUBCHANNEL when MODIFY
SUBCHANNEL sets condition code 0. Use of
STORE SUBCHANNEL is a method for deter-
mining if the designated subchannel was
changed or not. Failure to inspect the subchan-
nel following the setting of condition code 0 by
MODIFY SUBCHANNEL may result in conditions
that the program does not expect to occur."
That's exactly what we had to do under z/VM back then: do the msch,
check via stsch, redo the msch if needed, check again via stsch. It
usually worked with the second msch the latest.
OK, I understand, then it is a bug in zVM that this test could enlighten.
I think we should keep it so, it allows to recognize 3 cases (after I
change to test ENABLE in the loop as I said I will):
- immediate ENABLE
- asynchrone ENABLE
- failure to ENABLE
and you probably should not delay on success?
yes, it is not optimized, I can test PMCW_ENABLE in the loop this way we
can see if, in the zVM case we need to do retries or not.
+ } while (!(pmcw->flags & PMCW_ENABLE) && count++ < 5);
How is this supposed to work? Doesn't the stsch overwrite the control
block again, so you need to re-set the enable bit before you retry?
I do not think so, there is no msch() in the loop.
Do I miss something?
Well, _I_ missed that the msch() was missing :) You need it (see above);
just waiting and re-doing the stsch is useless, as msch is a
synchronous instruction which has finished its processing after the cc
has been set.
Since kvm-unit-test is a test system, not an OS so I think that here we
have one more point to leverage the enable function:
- We need to test the enable (what I did (partially))
- We need the enable to work (your proposition) to further test the I/O
OK, I rework this part with your comment in mind.
Thanks
Pierre
--
Pierre Morel
IBM Lab Boeblingen
