Eli Dorfman (Voltaire) wrote:
Yevgeny Kliteynik wrote:
Eli Dorfman (Voltaire) wrote:
Yevgeny Kliteynik wrote:
Eli Dorfman (Voltaire) wrote:
Yevgeny Kliteynik wrote:
Yevgeny Kliteynik wrote:
Line Holen wrote:
On 11/ 4/09 04:54 PM, Yevgeny Kliteynik wrote:
Line Holen wrote:
On 11/ 4/09 10:47 AM, Yevgeny Kliteynik wrote:
Sasha Khapyorsky wrote:
On 12:26 Tue 03 Nov , Yevgeny Kliteynik wrote:
Always do heavy sweep when there is only one node in the
fabric, and this node is a switch, and SM runs on top of it -
there may be a race when OSM starts running before the
external ports are ports are up, or if they went through
reset while SM was starting.
In this race switch brings up the ports and turns on the
PSC bit, but OSM might get PortInfo before SwitchInfo, and it
might see all ports as down, but PSC bit on. If that happens,
OSM turns off PSC bit, and it will never see external ports
again - it won't perform any heavy sweep, only light sweep
Could such race happen when there are more than one node in a
fabric?
I think that my description of the race was misleading.
The race can happen on *any* fabric when SM runs on switch.
But when it does happen, SM thinks that the whole subnet
is just one switch - that's what it managed to discover.
I've actually seen it happening.
So the patch fixes this particular case.
So the next question that you would probably ask is can
this race happen on some *other* switch and not the one
SM is running on?
Well, I don't know. I have a hunch that it can't, but I
couldn't prove it to myself yet.
The race on the managed switch is a special case because
SM always sees port 0, and always gets responses to its
SMP queries. On any other switch, if the ports were reset,
SM won't get any response until the ports are up again.
Perhaps there might be a case where SM got some port as down,
and by the time SM got SwitchInfo with PSC bit the port
was already up, so SM won't start discovery beyond this
port. But this race would be fixed on the next heavy sweep,
when SM will discover this port that it missed the previous
time, whereas race on managed switch is fatal - SM won't
ever do any heavy sweep.
-- Yevgeny
At least for the 3.2 branch there is a general race regardless of
where the SM is running. I haven't checked the current master, but
I cannot recall seeing any patches related to this so I assume
the race is still there.
There is a window between SM discovering a switch and clearing PSC
for the same switch. The SM will not detect a state change on the
switch ports during this time.
If the port changes state during that period, the switch issues
new trap 128, which (I think) should cause SM to re-discover the
fabric once this discovery cycle is over. Is this correct?
I think the switch shall send a trap whenever it sets the PSC bit.
Once set I believe it will not send another trap until it is reset.
Or do I misinterpret the spec ?
I may be wrong, but I thought that this is how things work:
- port state changes
- switch turns on PSC bit and starts sending traps
- SM gets the trap, sends trap repress
- switch gets trap repress and stops sending traps
- PSC is still on
- port state changes again (the same or any other port)
- switch turns on PSC bit (which doesn't matter as PSC is
already on) and starts sending traps again
- etc...
Anyway, I'll double-check this issue.
Yep, verified.
Switch sends traps regardless the PSC bit status.
Also, the spec doesn't link them together:
o14-5.1.1: If a switch supports Traps (PortInfo:
CapabilityMask.IsTrap-Supported is one), its SMA
shall send trap 128 to the SM indicated by the
PortInfo:MasterSMLID
under any condition that would cause SwitchInfo:PortStateChange to
be set
to one. (See 14.2.5.4 SwitchInfo on page 827.)
Trap will be sent according to the SMLID. After first bring up the
SMLID is not set yet and trap will not be sent.
In that case the opensm would discover the change only by PSC bit.
For IS3 chips the PSC bit and/or trap were set only after one or more
ports changed their state, so I don't understand how can the SM
discover PSC bit set while all ports are down. Or is this a change in
IS4?
It can happen when SM runs on the switch, not not host.
In this case if all ports are going down, SM will see
them all down and it will see PSC bit on.
So this patch is only for SM running on a switch which is the only
node in the fabric?
I don't see the race when there is more than one switch - please explain.
Quoting from above:
The race can happen on *any* fabric when SM runs on switch.
But when it does happen, SM thinks that the whole subnet
is just one switch - that's what it managed to discover.
I saw that but I don't understand how this can happen.
If PSC bit is set after *every* port state change and
SM clears PSC bit before reading PortInfo from the switch,
osm_node_info_rcv.c, ni_rcv_process_switch():
I see in the code that SM receives NodeInfo, then it requests
SwitchInfo and right after that it requests PortInfo for all
the ports w/o waiting for the SwitchInfo response.
In addition to that, if it happens during the first master
sweep, SM LID is not configured yet, or configured to the
wrong value, so no traps will be received by the SM.
-- Yevgeny
then there is no race condition.
As I mentioned before for IS3 switches that is correct.
Is there a different behavior with IS4 switches?
Also AFAIK the PSC bit is set only after any physical port state change.
Yes, but it is set only once.
PSC bit should be set after *every* port state change.
Eli
Meanwhile, the ports can change from up to down,
then SM discovers them, and then from down to up.
-- Yevgeny
So if we clear the PSC bit and only then get PortInfo we will still
catch any new state change.
right?
Eli
-- Yevgeny
Eli
-- Yevgeny
-- Yevgeny
Or perhaps the more serious problem happens when SM LID is not
configured yet on the switch, hence the trap is not going to the
right place?
I have a patch for the 3.2 branch that I can merge into master.
Sure, that would be nice :)
-- Yevgeny
Line
Sasha
Signed-off-by: Yevgeny Kliteynik <klit...@dev.mellanox.co.il>
---
opensm/opensm/osm_state_mgr.c | 15 ++++++++++-----
1 files changed, 10 insertions(+), 5 deletions(-)
diff --git a/opensm/opensm/osm_state_mgr.c
b/opensm/opensm/osm_state_mgr.c
index 4303d6e..537c855 100644
--- a/opensm/opensm/osm_state_mgr.c
+++ b/opensm/opensm/osm_state_mgr.c
@@ -1062,13 +1062,18 @@ static void do_sweep(osm_sm_t * sm)
* Otherwise, this is probably our first discovery pass
* or we are connected in loopback. In both cases do a
* heavy sweep.
- * Note: If we are connected in loopback we want a heavy
- * sweep, since we will not be getting any traps if
there is
- * a lost connection.
+ * Note the following:
+ * 1. If we are connected in loopback we want a heavy
sweep,
since we
+ * will not be getting any traps if there is a lost
connection.
+ * 2. If we are in DISCOVERING state - this means it is
either in
+ * initializing or wake up from STANDBY - run the heavy
sweep.
+ * 3. If there is only one node in the fabric, and this
node is a
+ * switch, and OSM runs on top of it, there might be a
race
when
+ * OSM starts running before the external ports are
up -
run the
+ * heavy sweep.
*/
- /* if we are in DISCOVERING state - this means it is
either in
- * initializing or wake up from STANDBY - run the heavy
sweep */
if (cl_qmap_count(&sm->p_subn->sw_guid_tbl)
+ && cl_qmap_count(&sm->p_subn->node_guid_tbl) != 1
&& sm->p_subn->sm_state != IB_SMINFO_STATE_DISCOVERING
&& sm->p_subn->opt.force_heavy_sweep == FALSE
&& sm->p_subn->force_heavy_sweep == FALSE
--
1.5.1.4
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