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SubjectRe: [RESEND] [PATCH] readahead:add blk_run_backing_dev

Ronald Moesbergen, on 07/17/2009 06:15 PM wrote:
> 2009/7/16 Vladislav Bolkhovitin <vst@vlnb.net>:
>> Ronald Moesbergen, on 07/16/2009 11:32 AM wrote:
>>> 2009/7/15 Vladislav Bolkhovitin <vst@vlnb.net>:
>>>>> The drop with 64 max_sectors_kb on the client is a consequence of how
>>>>> CFQ
>>>>> is working. I can't find the exact code responsible for this, but from
>>>>> all
>>>>> signs, CFQ stops delaying requests if amount of outstanding requests
>>>>> exceeds
>>>>> some threshold, which is 2 or 3. With 64 max_sectors_kb and 5 SCST I/O
>>>>> threads this threshold is exceeded, so CFQ doesn't recover order of
>>>>> requests, hence the performance drop. With default 512 max_sectors_kb
>>>>> and
>>>>> 128K RA the server sees at max 2 requests at time.
>>>>>
>>>>> Ronald, can you perform the same tests with 1 and 2 SCST I/O threads,
>>>>> please?
>>> Ok. Should I still use the file-on-xfs testcase for this, or should I
>>> go back to using a regular block device?
>> Yes, please
>>
>>> The file-over-iscsi is quite
>>> uncommon I suppose, most people will export a block device over iscsi,
>>> not a file.
>> No, files are common. The main reason why people use direct block devices is
>> a not supported by anything believe that comparing with files they "have
>> less overhead", so "should be faster". But it isn't true and can be easily
>> checked.
>>
>>>> With context-RA patch, please, in those and future tests, since it should
>>>> make RA for cooperative threads much better.
>>>>
>>>>> You can limit amount of SCST I/O threads by num_threads parameter of
>>>>> scst_vdisk module.
>>> Ok, I'll try that and include the blk_run_backing_dev,
>>> readahead-context and io_context patches.
>
> The results:
>
> client kernel: 2.6.26-15lenny3 (debian)
> server kernel: 2.6.29.5 with readahead-context, blk_run_backing_dev
> and io_context
>
> With one IO thread:
>
> 5) client: default, server: default
> blocksize R R R R(avg, R(std R
> (bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
> 67108864 15.990 15.308 16.689 64.097 2.259 1.002
> 33554432 15.981 16.064 16.221 63.651 0.392 1.989
> 16777216 15.841 15.660 16.031 64.635 0.619 4.040
>
> 6) client: default, server: 64 max_sectors_kb, RA default
> blocksize R R R R(avg, R(std R
> (bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
> 67108864 16.035 16.024 16.654 63.084 1.130 0.986
> 33554432 15.924 15.975 16.359 63.668 0.762 1.990
> 16777216 16.168 16.104 15.838 63.858 0.571 3.991
>
> 7) client: default, server: default max_sectors_kb, RA 2MB
> blocksize R R R R(avg, R(std R
> (bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
> 67108864 14.895 16.142 15.998 65.398 2.379 1.022
> 33554432 16.753 16.169 16.067 62.729 1.146 1.960
> 16777216 16.866 15.912 16.099 62.892 1.570 3.931
>
> 8) client: default, server: 64 max_sectors_kb, RA 2MB
> blocksize R R R R(avg, R(std R
> (bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
> 67108864 15.923 15.716 16.741 63.545 1.715 0.993
> 33554432 16.010 16.026 16.113 63.802 0.180 1.994
> 16777216 16.644 16.239 16.143 62.672 0.827 3.917
>
> 9) client: 64 max_sectors_kb, default RA. server: 64 max_sectors_kb, RA 2MB
> blocksize R R R R(avg, R(std R
> (bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
> 67108864 15.753 15.882 15.482 65.207 0.697 1.019
> 33554432 15.670 16.268 15.669 64.548 1.134 2.017
> 16777216 15.746 15.519 16.411 64.471 1.516 4.029
>
> 10) client: default max_sectors_kb, 2MB RA. server: 64 max_sectors_kb, RA 2MB
> blocksize R R R R(avg, R(std R
> (bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
> 67108864 13.639 14.360 13.654 73.795 1.758 1.153
> 33554432 13.584 13.938 14.538 73.095 2.035 2.284
> 16777216 13.617 13.510 13.803 75.060 0.665 4.691
>
> 11) client: 64 max_sectors_kb, 2MB. RA server: 64 max_sectors_kb, RA 2MB
> blocksize R R R R(avg, R(std R
> (bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
> 67108864 13.428 13.541 14.144 74.760 1.690 1.168
> 33554432 13.707 13.352 13.462 75.821 0.827 2.369
> 16777216 14.380 13.504 13.675 73.975 1.991 4.623
>
> With two threads:
> 5) client: default, server: default
> blocksize R R R R(avg, R(std R
> (bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
> 67108864 12.453 12.173 13.014 81.677 2.254 1.276
> 33554432 12.066 11.999 12.960 83.073 2.877 2.596
> 16777216 13.719 11.969 12.569 80.554 4.500 5.035
>
> 6) client: default, server: 64 max_sectors_kb, RA default
> blocksize R R R R(avg, R(std R
> (bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
> 67108864 12.886 12.201 12.147 82.564 2.198 1.290
> 33554432 12.344 12.928 12.007 82.483 2.504 2.578
> 16777216 12.380 11.951 13.119 82.151 3.141 5.134
>
> 7) client: default, server: default max_sectors_kb, RA 2MB
> blocksize R R R R(avg, R(std R
> (bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
> 67108864 12.824 13.485 13.534 77.148 1.913 1.205
> 33554432 12.084 13.752 12.111 81.251 4.800 2.539
> 16777216 12.658 13.035 11.196 83.640 5.612 5.227
>
> 8) client: default, server: 64 max_sectors_kb, RA 2MB
> blocksize R R R R(avg, R(std R
> (bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
> 67108864 12.253 12.552 11.773 84.044 2.230 1.313
> 33554432 13.177 12.456 11.604 82.723 4.316 2.585
> 16777216 12.471 12.318 13.006 81.324 1.878 5.083
>
> 9) client: 64 max_sectors_kb, default RA. server: 64 max_sectors_kb, RA 2MB
> blocksize R R R R(avg, R(std R
> (bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
> 67108864 14.409 13.311 14.278 73.238 2.624 1.144
> 33554432 14.665 14.260 14.080 71.455 1.211 2.233
> 16777216 14.179 14.810 14.640 70.438 1.303 4.402
>
> 10) client: default max_sectors_kb, 2MB RA. server: 64 max_sectors_kb, RA 2MB
> blocksize R R R R(avg, R(std R
> (bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
> 67108864 13.401 14.107 13.549 74.860 1.642 1.170
> 33554432 14.575 13.221 14.428 72.894 3.236 2.278
> 16777216 13.771 14.227 13.594 73.887 1.408 4.618
>
> 11) client: 64 max_sectors_kb, 2MB. RA server: 64 max_sectors_kb, RA 2MB
> blocksize R R R R(avg, R(std R
> (bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
> 67108864 10.286 12.272 10.245 94.317 7.690 1.474
> 33554432 10.241 10.415 13.374 91.624 10.670 2.863
> 16777216 10.499 10.224 10.792 97.526 2.151 6.095
>
> The last result comes close to 100MB/s!

Good! Although I expected maximum with a single thread.

Can you do the same set of tests with deadline scheduler on the server?

Thanks,
Vlad



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