[LU-11441] obd_get_mod_rpc_slot: run FIFO wait queue Created: 27/Sep/18  Updated: 10/Oct/18  Resolved: 10/Oct/18

Status: Resolved
Project: Lustre
Component/s: None
Affects Version/s: None
Fix Version/s: Lustre 2.12.0

Type: Bug Priority: Minor
Reporter: Vladimir Saveliev Assignee: Vladimir Saveliev
Resolution: Fixed Votes: 0
Labels: None

Attachments: Text File 0001-LU-11441-obdclass-make-mod-rpc-slot-wait-queue-FIFO.patch    
Severity: 3
Rank (Obsolete): 9223372036854775807

 Description   

Under relatively big load a process may spin in obd_get_mod_rpc_slot() for a long time
without successful grabbing a free mod rpc slot. It has been observed
a process spinning more than 100 seconds. See excerpt from lustre logs below. That test ran 72 mdtest-s and 8 IOR-s.

00000020:00100000:12.0:1534800918.648481:0:5506:0:(genops.c:2572:obd_get_mod_rpc_slot()) fs1-MDT0000-mdc-ffff88105b2f9000: sleeping for a modify RPC slot opc 101, max 7
...
00000020:00100000:28.0:1534800934.002775:0:5506:0:(genops.c:2572:obd_get_mod_rpc_slot()) fs1-MDT0000-mdc-ffff88105b2f9000: sleeping for a modify RPC slot opc 101, max 7
...
00000020:00100000:12.0:1534800972.382794:0:5506:0:(genops.c:2572:obd_get_mod_rpc_slot()) fs1-MDT0000-mdc-ffff88105b2f9000: sleeping for a modify RPC slot opc 101, max 7
...
00000020:00100000:31.0:1534801033.373093:0:5506:0:(genops.c:2572:obd_get_mod_rpc_slot()) fs1-MDT0000-mdc-ffff88105b2f9000: sleeping for a modify RPC slot opc 101, max 7

It might make sense for obd_get_mod_rpc_slot () to run FIFO wait queue.

 Comments   
Comment by Vladimir Saveliev [ 02/Oct/18 ]

Attached the patch here because for unknown reasons git push started to fail for me with:

 ! [remote rejected]       HEAD -> refs/for/master (not Signed-off-by author/committer/uploader in commit message footer)
error: failed to push some refs to 'ssh://vla@review.whamcloud.com:29418/fs/lustre-release'
Comment by Gerrit Updater [ 04/Oct/18 ]

Alexander Zarochentsev (c17826@cray.com) uploaded a new patch: https://review.whamcloud.com/33282
Subject: LU-11441 obdclass: make mod rpc slot wait queue FIFO
Project: fs/lustre-release
Branch: master
Current Patch Set: 1
Commit: 15bc6978fbbaee0ca003e1eea57e5fc45ec1950d

Comment by Gerrit Updater [ 10/Oct/18 ]

Oleg Drokin (green@whamcloud.com) merged in patch https://review.whamcloud.com/33282/
Subject: LU-11441 obdclass: make mod rpc slot wait queue FIFO
Project: fs/lustre-release
Branch: master
Current Patch Set:
Commit: 7fa0fd41577001629f7ecc418cfe814a46207148

Comment by Peter Jones [ 10/Oct/18 ]

Landed for 2.12

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