[Linux-cluster] optimising DLM speed?
Alan Brown
ajb2 at mssl.ucl.ac.uk
Thu Feb 24 12:56:10 UTC 2011
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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