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

Ronald Moesbergen
2009-07-03T09:14:20Z

2009/6/30 Vladislav Bolkhovitin <vst@vlnb.net>:
> Wu Fengguang, on 06/30/2009 05:04 AM wrote:
>>
>> On Mon, Jun 29, 2009 at 11:37:41PM +0800, Vladislav Bolkhovitin wrote:
>>>
>>> Wu Fengguang, on 06/29/2009 07:01 PM wrote:
>>>>
>>>> On Mon, Jun 29, 2009 at 10:21:24PM +0800, Wu Fengguang wrote:
>>>>>
>>>>> On Mon, Jun 29, 2009 at 10:00:20PM +0800, Ronald Moesbergen wrote:
>>>>>>
>>>>>> ... tests ...
>>>>>>
>>>>>>> We started with 2.6.29, so why not complete with it (to save
>>>>>>> additional
>>>>>>> Ronald's effort to move on 2.6.30)?
>>>>>>>
>>>>>>>>> 2. Default vanilla 2.6.29 kernel, 512 KB read-ahead, the rest is
>>>>>>>>> default
>>>>>>>>
>>>>>>>> How about 2MB RAID readahead size? That transforms into about 512KB
>>>>>>>> per-disk readahead size.
>>>>>>>
>>>>>>> OK. Ronald, can you 4 more test cases, please:
>>>>>>>
>>>>>>> 7. Default vanilla 2.6.29 kernel, 2MB read-ahead, the rest is default
>>>>>>>
>>>>>>> 8. Default vanilla 2.6.29 kernel, 2MB read-ahead, 64 KB
>>>>>>> max_sectors_kb, the rest is default
>>>>>>>
>>>>>>> 9. Patched by the Fengguang's patch vanilla 2.6.29 kernel, 2MB
>>>>>>> read-ahead, the rest is default
>>>>>>>
>>>>>>> 10. Patched by the Fengguang's patch vanilla 2.6.29 kernel, 2MB
>>>>>>> read-ahead, 64 KB max_sectors_kb, the rest is default
>>>>>>
>>>>>> The results:
>>>>>
>>>>> I made a blindless average:
>>>>>
>>>>> N       MB/s          IOPS      case
>>>>>
>>>>> 0      114.859       984.148    Unpatched, 128KB readahead, 512
>>>>> max_sectors_kb
>>>>> 1      122.960       981.213    Unpatched, 512KB readahead, 512
>>>>> max_sectors_kb
>>>>> 2      120.709       985.111    Unpatched, 2MB readahead, 512
>>>>> max_sectors_kb
>>>>> 3      158.732      1004.714    Unpatched, 512KB readahead, 64
>>>>> max_sectors_kb
>>>>> 4      159.237       979.659    Unpatched, 2MB readahead, 64
>>>>> max_sectors_kb
>>>>>
>>>>> 5      114.583       982.998    Patched, 128KB readahead, 512
>>>>> max_sectors_kb
>>>>> 6      124.902       987.523    Patched, 512KB readahead, 512
>>>>> max_sectors_kb
>>>>> 7      127.373       984.848    Patched, 2MB readahead, 512
>>>>> max_sectors_kb
>>>>> 8      161.218       986.698    Patched, 512KB readahead, 64
>>>>> max_sectors_kb
>>>>> 9      163.908       574.651    Patched, 2MB readahead, 64
>>>>> max_sectors_kb
>>>>>
>>>>> So before/after patch:
>>>>>
>>>>>        avg throughput      135.299 => 138.397  by +2.3%
>>>>>        avg IOPS            986.969 => 903.344  by -8.5%
>>>>>
>>>>> The IOPS is a bit weird.
>>>>>
>>>>> Summaries:
>>>>> - this patch improves RAID throughput by +2.3% on average
>>>>> - after this patch, 2MB readahead performs slightly better
>>>>>  (by 1-2%) than 512KB readahead
>>>>
>>>> and the most important one:
>>>> - 64 max_sectors_kb performs much better than 256 max_sectors_kb, by
>>>> ~30% !
>>>
>>> Yes, I've just wanted to point it out ;)
>>
>> OK, now I tend to agree on decreasing max_sectors_kb and increasing
>> read_ahead_kb. But before actually trying to push that idea I'd like
>> to
>> - do more benchmarks
>> - figure out why context readahead didn't help SCST performance
>>  (previous traces show that context readahead is submitting perfect
>>   large io requests, so I wonder if it's some io scheduler bug)
>
> Because, as we found out, without your http://lkml.org/lkml/2009/5/21/319
> patch read-ahead was nearly disabled, hence there were no difference which
> algorithm was used?
>
> Ronald, can you run the following tests, please? This time with 2 hosts,
> initiator (client) and target (server) connected using 1 Gbps iSCSI. It
> would be the best if on the client vanilla 2.6.29 will be ran, but any other
> kernel will be fine as well, only specify which. Blockdev-perftest should be
> ran as before in buffered mode, i.e. with "-a" switch.
>
> 1. All defaults on the client, on the server vanilla 2.6.29 with Fengguang's
> http://lkml.org/lkml/2009/5/21/319 patch with all default settings.
>
> 2. All defaults on the client, on the server vanilla 2.6.29 with Fengguang's
> http://lkml.org/lkml/2009/5/21/319 patch with default RA size and 64KB
> max_sectors_kb.
>
> 3. All defaults on the client, on the server vanilla 2.6.29 with Fengguang's
> http://lkml.org/lkml/2009/5/21/319 patch with 2MB RA size and default
> max_sectors_kb.
>
> 4. All defaults on the client, on the server vanilla 2.6.29 with Fengguang's
> http://lkml.org/lkml/2009/5/21/319 patch with 2MB RA size and 64KB
> max_sectors_kb.
>
> 5. All defaults on the client, on the server vanilla 2.6.29 with Fengguang's
> http://lkml.org/lkml/2009/5/21/319 patch and with context RA patch. RA size
> and max_sectors_kb are default. For your convenience I committed the
> backported context RA patches into the SCST SVN repository.
>
> 6. All defaults on the client, on the server vanilla 2.6.29 with Fengguang's
> http://lkml.org/lkml/2009/5/21/319 and context RA patches with default RA
> size and 64KB max_sectors_kb.
>
> 7. All defaults on the client, on the server vanilla 2.6.29 with Fengguang's
> http://lkml.org/lkml/2009/5/21/319 and context RA patches with 2MB RA size
> and default max_sectors_kb.
>
> 8. All defaults on the client, on the server vanilla 2.6.29 with Fengguang's
> http://lkml.org/lkml/2009/5/21/319 and context RA patches with 2MB RA size
> and 64KB max_sectors_kb.
>
> 9. On the client default RA size and 64KB max_sectors_kb. On the server
> vanilla 2.6.29 with Fengguang's http://lkml.org/lkml/2009/5/21/319 and
> context RA patches with 2MB RA size and 64KB max_sectors_kb.
>
> 10. On the client 2MB RA size and default max_sectors_kb. On the server
> vanilla 2.6.29 with Fengguang's http://lkml.org/lkml/2009/5/21/319 and
> context RA patches with 2MB RA size and 64KB max_sectors_kb.
>
> 11. On the client 2MB RA size and 64KB max_sectors_kb. On the server vanilla
> 2.6.29 with Fengguang's http://lkml.org/lkml/2009/5/21/319 and context RA
> patches with 2MB RA size and 64KB max_sectors_kb.

Ok, done. Performance is pretty bad overall :(

The kernels I used:
client kernel: 2.6.26-15lenny3 (debian)
server kernel: 2.6.29.5 with blk_dev_run patch

And I adjusted the blockdev-perftest script to drop caches on both the
server (via ssh) and the client.

The results:

1) client: default, server: default
blocksize R R R R(avg, R(std R
(bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
67108864 19.808 20.078 20.180 51.147 0.402 0.799
33554432 19.162 19.952 20.375 51.673 1.322 1.615
16777216 19.714 20.331 19.948 51.214 0.649 3.201
8388608 18.572 20.126 20.345 52.116 2.149 6.515
4194304 18.711 19.663 19.811 52.831 1.350 13.208
2097152 19.112 19.927 19.130 52.832 1.022 26.416
1048576 19.771 19.686 20.010 51.661 0.356 51.661
524288 19.585 19.940 19.483 52.065 0.515 104.131
262144 19.168 20.794 19.605 51.634 1.757 206.535
131072 19.077 20.776 20.271 51.160 1.849 409.282
65536 19.643 21.230 19.144 51.284 2.227 820.549
32768 19.702 20.869 19.686 51.020 1.380 1632.635
16384 21.218 20.222 20.221 49.846 1.121 3190.174

2) client: default, server: 64 max_sectors_kb
blocksize R R R R(avg, R(std R
(bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
67108864 20.881 20.102 21.689 49.065 1.522 0.767
33554432 20.329 19.938 20.522 50.543 0.609 1.579
16777216 20.247 19.744 20.912 50.468 1.185 3.154
8388608 19.739 20.184 21.032 50.433 1.318 6.304
4194304 19.968 18.748 20.230 52.174 1.750 13.043
2097152 19.633 20.068 19.858 51.584 0.462 25.792
1048576 20.552 20.618 20.974 49.437 0.440 49.437
524288 21.595 20.830 20.454 48.881 1.098 97.762
262144 21.720 20.602 20.176 49.201 1.515 196.805
131072 20.976 19.089 20.712 50.634 2.144 405.072
65536 20.661 19.952 19.312 51.303 1.414 820.854
32768 21.155 18.464 20.640 51.159 3.081 1637.090
16384 22.023 19.944 20.629 49.159 2.008 3146.205

3) 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 21.709 19.315 18.319 52.028 3.631 0.813
33554432 20.745 19.209 19.048 52.142 1.976 1.629
16777216 19.762 19.175 19.485 52.591 0.649 3.287
8388608 19.812 19.142 19.574 52.498 0.749 6.562
4194304 19.931 19.786 19.505 51.877 0.466 12.969
2097152 19.473 19.208 19.438 52.859 0.322 26.430
1048576 19.524 19.033 19.477 52.941 0.610 52.941
524288 20.115 20.402 19.542 51.166 0.920 102.333
262144 19.291 19.715 21.016 51.249 1.844 204.996
131072 18.782 19.130 20.334 52.802 1.775 422.419
65536 19.030 19.233 20.328 52.475 1.504 839.599
32768 19.147 19.326 19.411 53.074 0.303 1698.357
16384 19.573 19.596 20.417 51.575 1.005 3300.788

4) 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 22.604 21.707 20.721 47.298 1.683 0.739
33554432 21.654 20.812 21.162 48.293 0.784 1.509
16777216 20.461 19.782 21.160 50.068 1.377 3.129
8388608 20.886 20.434 21.512 48.914 1.028 6.114
4194304 22.154 20.512 21.433 47.974 1.517 11.993
2097152 22.258 20.971 20.738 48.071 1.478 24.035
1048576 19.953 21.294 19.662 50.497 1.731 50.497
524288 21.577 20.884 20.883 48.509 0.743 97.019
262144 20.959 20.749 20.256 49.587 0.712 198.347
131072 19.926 21.542 19.634 50.360 2.022 402.877
65536 20.973 22.546 20.840 47.793 1.685 764.690
32768 20.695 21.031 21.182 48.837 0.476 1562.791
16384 20.163 21.112 20.037 50.133 1.159 3208.481

5) Server RA-context Patched, client: default, server: default
blocksize R R R R(avg, R(std R
(bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
67108864 19.756 23.647 18.852 49.818 4.717 0.778
33554432 18.892 19.727 18.857 53.472 1.106 1.671
16777216 18.943 19.255 18.949 53.760 0.409 3.360
8388608 18.766 19.105 18.847 54.165 0.413 6.771
4194304 19.177 19.609 20.191 52.111 1.097 13.028
2097152 18.968 19.517 18.862 53.581 0.797 26.790
1048576 18.833 19.912 18.626 53.592 1.551 53.592
524288 19.128 19.379 19.134 53.298 0.324 106.596
262144 18.955 19.328 18.879 53.748 0.550 214.992
131072 18.401 19.642 18.928 53.961 1.439 431.691
65536 19.366 19.822 18.615 53.182 1.384 850.908
32768 19.252 19.229 18.752 53.683 0.653 1717.857
16384 21.373 19.507 19.162 51.282 2.415 3282.039

6) Server RA-context Patched, 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 22.753 21.071 20.532 47.825 2.061 0.747
33554432 20.404 19.239 20.722 50.943 1.644 1.592
16777216 20.914 20.114 21.854 48.910 1.655 3.057
8388608 19.524 21.932 21.465 48.949 2.510 6.119
4194304 20.306 20.809 20.000 50.279 0.820 12.570
2097152 20.133 20.194 20.181 50.770 0.066 25.385
1048576 19.515 21.593 20.052 50.321 2.128 50.321
524288 20.231 20.502 20.299 50.335 0.284 100.670
262144 19.620 19.737 19.911 51.834 0.313 207.336
131072 20.486 21.138 22.339 48.089 1.711 384.714
65536 20.113 18.322 22.247 50.943 4.025 815.088
32768 23.341 23.328 20.809 45.659 2.511 1461.089
16384 20.962 21.839 23.405 46.496 2.100 2975.773

7) Server RA-context Patched, 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 19.565 19.028 19.164 53.196 0.627 0.831
33554432 19.048 18.401 18.940 54.491 0.828 1.703
16777216 18.728 19.330 19.076 53.778 0.699 3.361
8388608 19.174 18.710 19.922 53.179 1.368 6.647
4194304 19.133 18.514 19.672 53.628 1.331 13.407
2097152 18.903 18.547 20.070 53.468 1.782 26.734
1048576 19.210 19.204 18.994 53.513 0.282 53.513
524288 18.978 18.723 20.839 52.596 2.464 105.192
262144 18.912 18.590 18.635 54.726 0.415 218.905
131072 18.732 18.578 19.797 53.837 1.505 430.694
65536 19.046 18.872 19.318 53.678 0.516 858.852
32768 18.490 18.582 20.374 53.583 2.353 1714.661
16384 19.138 19.215 20.602 52.167 1.744 3338.700

8) Server RA-context Patched, 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 21.029 21.654 21.093 48.177 0.630 0.753
33554432 21.174 19.759 20.659 49.918 1.435 1.560
16777216 20.385 20.235 22.145 49.026 1.976 3.064
8388608 19.053 20.162 20.158 51.778 1.391 6.472
4194304 20.123 23.173 20.073 48.696 3.188 12.174
2097152 19.401 20.824 20.326 50.778 1.500 25.389
1048576 21.821 21.401 21.026 47.825 0.724 47.825
524288 21.478 20.742 21.355 48.332 0.742 96.664
262144 20.290 20.183 20.980 50.004 0.853 200.015
131072 20.299 21.501 20.766 49.127 1.158 393.020
65536 21.087 19.340 20.867 50.193 1.959 803.092
32768 21.597 21.223 23.504 46.410 2.039 1485.132
16384 21.681 21.709 22.944 46.343 1.212 2965.967

9) Server RA-context Patched, 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 42.767 40.615 41.188 24.672 0.535 0.386
33554432 41.204 42.294 40.514 24.780 0.437 0.774
16777216 39.774 42.809 41.804 24.720 0.762 1.545
8388608 42.292 41.799 40.386 24.689 0.486 3.086
4194304 41.784 39.037 41.830 25.073 0.819 6.268
2097152 41.983 41.145 44.115 24.164 0.703 12.082
1048576 41.468 43.495 41.640 24.276 0.520 24.276
524288 42.631 42.724 41.267 24.267 0.387 48.535
262144 41.930 41.954 41.975 24.408 0.011 97.634
131072 42.511 41.266 42.835 24.269 0.393 194.154
65536 41.307 41.544 40.746 24.857 0.203 397.704
32768 42.270 42.728 40.822 24.425 0.478 781.607
16384 39.307 40.044 40.259 25.686 0.264 1643.908
8192 41.258 40.879 40.969 24.955 0.098 3194.183

10) Server RA-context Patched, 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 26.160 26.878 25.790 38.982 0.666 0.609
33554432 25.832 25.362 25.695 39.956 0.309 1.249
16777216 26.119 24.769 25.526 40.221 0.876 2.514
8388608 25.660 26.257 25.106 39.898 0.730 4.987
4194304 26.603 25.404 25.271 39.773 0.910 9.943
2097152 26.012 24.815 26.064 39.973 0.914 19.986
1048576 25.256 27.073 25.153 39.693 1.323 39.693
524288 29.452 28.883 29.146 35.118 0.280 70.236
262144 26.559 27.315 26.837 38.067 0.440 152.268
131072 25.259 25.794 25.992 39.879 0.483 319.030
65536 26.417 25.205 26.177 39.503 0.808 632.047
32768 26.453 26.401 25.759 39.083 0.474 1250.669
16384 24.701 24.609 25.143 41.265 0.385 2640.945

11) Server RA-context Patched, 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 29.629 31.703 30.407 33.513 0.930 0.524
33554432 29.768 29.598 30.717 34.111 0.553 1.066
16777216 30.054 30.640 30.102 33.837 0.295 2.115
8388608 29.906 29.744 31.394 33.762 0.813 4.220
4194304 30.708 30.797 30.418 33.420 0.177 8.355
2097152 31.364 29.646 30.712 33.511 0.781 16.755
1048576 30.757 30.600 30.470 33.455 0.128 33.455
524288 29.715 31.176 29.977 33.822 0.701 67.644
262144 30.533 30.218 30.259 33.755 0.155 135.021
131072 30.403 32.609 30.651 32.831 1.016 262.645
65536 30.846 30.208 32.116 32.993 0.835 527.889
32768 30.526 29.794 30.556 33.809 0.397 1081.878
16384 31.560 31.532 30.938 32.673 0.301 2091.092

Ronald.