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Re: [Linux-cluster] optimising DLM speed?



Steven Whitehouse wrote:

That doesn't sound like it is related to a DLM issue. 150 entries is not
a lot.

It isn't, but when the machine's being hammered by requests in other filesystems, things can get very slow, very quickly.

What do you mean be "access" in this case? Just looking up a
single file in the directory, or create/delete files or an ls -l
(implying stats to each file) or what exactly?

ls -l and creation/deletion.



Again, figuring out the exact workload should help us get to the bottom
of what is going on here. How are you measuring the delays reported
above? Is the syscall service time, for example?

iostats.

This is a typcal example. Note the huge difference between await (total time in ms) and svctm (scsi command response time in ms)


avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.62    0.00    2.12   27.03    0.00   70.22

Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util dm-6 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 dm-7 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 dm-8 0.00 0.00 16.00 1.00 8.00 0.50 1.00 0.20 11.47 11.47 19.50 dm-9 0.00 0.00 45.00 22.00 180.00 88.00 8.00 13.45 351.07 6.19 41.50 dm-10 0.00 0.00 61.00 30.00 244.00 120.00 8.00 22.19 307.56 10.19 92.70 dm-11 0.00 0.00 53.00 5.00 212.00 20.00 8.00 128.12 4332.69 17.26 100.10 dm-12 0.00 0.00 54.00 0.00 216.00 0.00 8.00 100.28 2951.09 18.54 100.10 dm-13 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 dm-14 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

For comparison here's a FC-attached box running Ext4 (on a slower set of arrays)


Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util dm-2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 dm-3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 dm-4 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 dm-5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 dm-6 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 dm-7 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 dm-8 0.00 0.00 247.00 0.00 988.00 0.00 8.00 19.17 92.43 3.28 81.10 dm-9 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 dm-10 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 dm-11 0.00 0.00 51.00 14.00 21548.00 56.00 664.74 1.93 29.91 4.14 26.90 dm-12 0.00 0.00 54.00 424.00 25800.00 1696.00 115.05 6.07 12.69 0.60 28.50 dm-13 0.00 0.00 55.00 0.00 23928.00 0.00 870.11 2.50 45.49 5.38 29.60 dm-14 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 dm-15 0.00 0.00 247.00 0.00 988.00 0.00 8.00 19.17 92.44 3.29 81.20 dm-16 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00





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