On Wednesday 12 June 2013 15:03:11 Christopher Samuel wrote: > Hi folks,
In my experience bad cables / unstable fabric (on FDR + CX3 clusters) show up by one or more of: * LinkDownedCounter ticking up * SymbolErrorCounter ticking up * ports at FDR10 not FDR (use for example iblinkinfo / ibdiagnet) PortXmitWait is expected to increase (a lot). Some ideas: * Use something simple but large scale to test IB before HPL. * Run HPL with show-as-you-go and plot that data (even but low == bad HPL config or low perf node / blas, uneven plot == bad fabric). * Run HPL on ethernet, you should be able to get >50% on 65 nodes unless your eth is too weak. * Make sure ranks are placed properly and consume expected amount of ram, also check pinning if used (top, lstopo --ps, taskset -p PID, ..). With your config you should be able to get to ~90% HPL efficiency. Cheers, Peter > I'm doing the bring up and testing on our SandyBridge IBM iDataplex > with an FDR switch and as part of that I've been doing burn-in testing > with HPL and seeing really poor efficiency (~25% over 65 odd nodes > with 256GB RAM). Simultaneously HPL on the 3 nodes with 512GB RAM > gives ~70% efficiency. > > Checking the switch with ibqueryerrors shows lots of things like: > > GUID 0x2c90300771450 port 22: [PortXmitWait == 198817026] > > That's about 2 or 3 hours after last clearing the counters. :-( > > Doing: > > # ibclearcounters && ibclearerrors && sleep 1 && ibqueryerrors > > Shows 75 of 94 nodes bad, pretty much all with thousands of > PortXmitWait, some into the 10's of thousands. > > We are running RHEL 6.3, Mellanox OFED 2.0.5, FDR IB and Open-MPI 1.6.4. > > Talking with another site who also has the same sort of iDataplex, but > running RHEL 5.8, Mellanox OFED 1.5 and QDR I, reveals that they (once > they started looking) are also seeing high PortXmitWait counters > shortly after clearing them with user codes. > > These are Mellanox MT27500 ConnectX-3 adapters. > > We're talking with both IBM and Mellanox directly, but other than > Mellanox spotting some GPFS NSD file servers that had bad FDR ports > (which got unplugged last week and fixed today) we've not made any > progress into the underlying cause. :-( > > Has anyone seen anything like this before? > > cheers! > Chris
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