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Date: Sat, 07 Feb 2009 06:30:22 +0000 From: "Gary L. Grobe" <gary@...be.net> To: linux-kernel@...r.kernel.org Subject: processes in D State too long too often I'm currently running 2.6.27-r7 with ether and myrinet interconnects on slave quad and dual-quad dell 1950's w/ 16-32Gb's ram and a master node that is a Dell 6850 w/ 32Gb. I've got processes running on diskless nodes mounted to a master node via NFS. I see that several of these processes are in a D state, yet they recover in a very short time back to running (a few seconds) and then the CPU goes from 0% to 100% usage (which is correct, these CPU's should be running @ 100% as they're running some number crunching simulations, but when in D state CPU usage goes to 0%). So why they are in a D state and waiting on I/O? Then I look on the master node and see that several nfsd's are also in a D state, and shortly recover back to running (I see this shown as '-' if using ps, or R in 'top'). Running 'ps -eal', I see in the WCHAN column for the processes in a D state the following (which I believe is what the processes are waiting on). It can be a mix of these. I usually see 'sync_p', 'nfs_wa', 'lmGrou', and 'txLock'. My file system type is JFS. Here's a snipped 'ps -eal' listing on the master node. 1 D 0 26709 2 0 75 -5 - 0 lmGrou ? 00:00:07 nfsd 1 S 0 26710 2 0 75 -5 - 0 - ? 00:00:07 nfsd 1 S 0 26711 2 0 75 -5 - 0 - ? 00:00:04 nfsd 1 S 0 26712 2 0 75 -5 - 0 - ? 00:00:08 nfsd 1 D 0 26713 2 0 75 -5 - 0 lmGrou ? 00:00:10 nfsd 1 S 0 26714 2 0 75 -5 - 0 - ? 00:00:09 nfsd 1 D 0 26715 2 0 75 -5 - 0 txLock ? 00:00:08 nfsd 1 D 0 26716 2 0 75 -5 - 0 - ? 00:00:09 nfsd 1 D 0 26717 2 0 75 -5 - 0 txLock ? 00:00:09 nfsd 1 S 0 26718 2 0 75 -5 - 0 - ? 00:00:07 nfsd 1 D 0 26719 2 0 75 -5 - 0 - ? 00:00:08 nfsd 1 D 0 26720 2 0 75 -5 - 0 sync_p ? 00:00:09 nfsd 1 S 0 26721 2 0 75 -5 - 0 - ? 00:00:09 nfsd 1 S 0 26722 2 0 75 -5 - 0 - ? 00:00:09 nfsd And here's the same command on a diskless node which shows that my processes are in a D state w/ what seems to be nfs_wait (and from which they recover quite quickly, a few seconds later) ... # ps -eal F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD ... 1 S 1001 6145 1 0 80 0 - 6560 924758 ? 00:00:01 orted 0 D 1001 6146 6145 71 80 0 - 941316 nfs_wa ? 19:27:10 lve_1 0 D 1001 6147 6145 58 80 0 - 894594 nfs_wa ? 15:57:56 lve_1 0 R 1001 6148 6145 57 80 0 - 901343 - ? 15:33:07 lve_1 0 R 1001 6149 6145 78 80 0 - 896065 - ? 21:31:32 lve_1 ... 'rpcinfo -p master_node' shows that I have portmapper, mountd, nlockmgr, and nfs running w/ all the correct normal info. It would seem as if NFS was dropping out intermittently, but I've really gone all throughout the NFS config and see nothing wrong, my DNS servers are working fine, it's all running on a local LAN (no firewall issues), and I see the same results on many different diskless nodes so I don't believe it's a hardware issues. All my previous installations have run fine w/ this same NFS config. Others have suggested this may be a 2.6.27-r7 kernel bug. I must note that I did not have this same problem running a 2.6.17 kernel w/ XFS. The hold up seems to be in the kernel and I'm looking for any advice is this might be the case. Because these processes are going into a D state so often, a simulation that might normally run for 6 hours now takes 2 days to complete. I've tested the myrinet and ether interconnects and I see no issues from node to node or switch. I can reproduce the problem every time between any one node and the master. So I'm looking for thoughts as to what might be going on and how to further investigate if this is in fact a kernel issue. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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