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

Ronald.


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