[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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