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

Vladislav Bolkhovitin
2009-07-06T11:13:15Z

(Restored the original list of recipients in this thread as I was asked.)

Hi Ronald,

Ronald Moesbergen, on 07/04/2009 07:19 PM wrote:
> 2009/7/3 Vladislav Bolkhovitin <vst@vlnb.net>:
>> Ronald Moesbergen, on 07/03/2009 01:14 PM wrote:
>>>>> 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:
>>>
>
> ... previous results ...
>
>> Those are on the server without io_context-2.6.29 and readahead-2.6.29
>> patches applied and with CFQ scheduler, correct?
>>
>> Then we see how reorder of requests caused by many I/O threads submitting
>> I/O in separate I/O contexts badly affect performance and no RA, especially
>> with default 128KB RA size, can solve it. Less max_sectors_kb on the client
>> => more requests it sends at once => more reorder on the server => worse
>> throughput. Although, Fengguang, in theory, context RA with 2MB RA size
>> should considerably help it, no?
>>
>> Ronald, can you perform those tests again with both io_context-2.6.29 and
>> readahead-2.6.29 patches applied on the server, please?
>
> Hi Vlad,
>
> I have retested with the patches you requested (and got access to the
> systems today :) ) The results are better, but still not great.
>
> client kernel: 2.6.26-15lenny3 (debian)
> server kernel: 2.6.29.5 with io_context and readahead patch
>
> 5) client: default, server: default
> blocksize R R R R(avg, R(std R
> (bytes) (s) (s) (s) MB/s) ,MB/s) (IOPS)
> 67108864 18.303 19.867 18.481 54.299 1.961 0.848
> 33554432 18.321 17.681 18.708 56.181 1.314 1.756
> 16777216 17.816 17.406 19.257 56.494 2.410 3.531
> 8388608 18.077 17.727 19.338 55.789 2.056 6.974
> 4194304 17.918 16.601 18.287 58.276 2.454 14.569
> 2097152 17.426 17.334 17.610 58.661 0.384 29.331
> 1048576 19.358 18.764 17.253 55.607 2.734 55.607
> 524288 17.951 18.163 17.440 57.379 0.983 114.757
> 262144 18.196 17.724 17.520 57.499 0.907 229.995
> 131072 18.342 18.259 17.551 56.751 1.131 454.010
> 65536 17.733 18.572 17.134 57.548 1.893 920.766
> 32768 19.081 19.321 17.364 55.213 2.673 1766.818
> 16384 17.181 18.729 17.731 57.343 2.033 3669.932
>
> 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 21.790 20.062 19.534 50.153 2.304 0.784
> 33554432 20.212 19.744 19.564 51.623 0.706 1.613
> 16777216 20.404 19.329 19.738 51.680 1.148 3.230
> 8388608 20.170 20.772 19.509 50.852 1.304 6.356
> 4194304 19.334 18.742 18.522 54.296 0.978 13.574
> 2097152 19.413 18.858 18.884 53.758 0.715 26.879
> 1048576 20.472 18.755 18.476 53.347 2.377 53.347
> 524288 19.120 20.104 18.404 53.378 1.925 106.756
> 262144 20.337 19.213 18.636 52.866 1.901 211.464
> 131072 19.199 18.312 19.970 53.510 1.900 428.083
> 65536 19.855 20.114 19.592 51.584 0.555 825.342
> 32768 20.586 18.724 20.340 51.592 2.204 1650.941
> 16384 21.119 19.834 19.594 50.792 1.651 3250.669
>
> 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 17.767 16.489 16.949 60.050 1.842 0.938
> 33554432 16.777 17.034 17.102 60.341 0.500 1.886
> 16777216 18.509 16.784 16.971 58.891 2.537 3.681
> 8388608 18.058 17.949 17.599 57.313 0.632 7.164
> 4194304 18.286 17.648 17.026 58.055 1.692 14.514
> 2097152 17.387 18.451 17.875 57.226 1.388 28.613
> 1048576 18.270 17.698 17.570 57.397 0.969 57.397
> 524288 16.708 17.900 17.233 59.306 1.668 118.611
> 262144 18.041 17.381 18.035 57.484 1.011 229.934
> 131072 17.994 17.777 18.146 56.981 0.481 455.844
> 65536 17.097 18.597 17.737 57.563 1.975 921.011
> 32768 17.167 17.035 19.693 57.254 3.721 1832.127
> 16384 17.144 16.664 17.623 59.762 1.367 3824.774
>
> 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 20.003 21.133 19.308 50.894 1.881 0.795
> 33554432 19.448 20.015 18.908 52.657 1.222 1.646
> 16777216 19.964 19.350 19.106 52.603 0.967 3.288
> 8388608 18.961 19.213 19.318 53.437 0.419 6.680
> 4194304 18.135 19.508 19.361 53.948 1.788 13.487
> 2097152 18.753 19.471 18.367 54.315 1.306 27.158
> 1048576 19.189 18.586 18.867 54.244 0.707 54.244
> 524288 18.985 19.199 18.840 53.874 0.417 107.749
> 262144 19.064 21.143 19.674 51.398 2.204 205.592
> 131072 18.691 18.664 19.116 54.406 0.594 435.245
> 65536 18.468 20.673 18.554 53.389 2.729 854.229
> 32768 20.401 21.156 19.552 50.323 1.623 1610.331
> 16384 19.532 20.028 20.466 51.196 0.977 3276.567
>
> 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 16.458 16.649 17.346 60.919 1.364 0.952
> 33554432 16.479 16.744 17.069 61.096 0.878 1.909
> 16777216 17.128 16.585 17.112 60.456 0.910 3.778
> 8388608 17.322 16.780 16.885 60.262 0.824 7.533
> 4194304 17.530 16.725 16.756 60.250 1.299 15.063
> 2097152 16.580 17.875 16.619 60.221 2.076 30.110
> 1048576 17.550 17.406 17.075 59.049 0.681 59.049
> 524288 16.492 18.211 16.832 59.718 2.519 119.436
> 262144 17.241 17.115 17.365 59.397 0.352 237.588
> 131072 17.430 16.902 17.511 59.271 0.936 474.167
> 65536 16.726 16.894 17.246 60.404 0.768 966.461
> 32768 16.662 17.517 17.052 59.989 1.224 1919.658
> 16384 17.429 16.793 16.753 60.285 1.085 3858.268
>
> 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 17.601 18.334 17.379 57.650 1.307 0.901
> 33554432 18.281 18.128 17.169 57.381 1.610 1.793
> 16777216 17.660 17.875 17.356 58.091 0.703 3.631
> 8388608 17.724 17.810 18.383 56.992 0.918 7.124
> 4194304 17.475 17.770 19.003 56.704 2.031 14.176
> 2097152 17.287 17.674 18.492 57.516 1.604 28.758
> 1048576 17.972 17.460 18.777 56.721 1.689 56.721
> 524288 18.680 18.952 19.445 53.837 0.890 107.673
> 262144 18.070 18.337 18.639 55.817 0.707 223.270
> 131072 16.990 16.651 16.862 60.832 0.507 486.657
> 65536 17.707 16.972 17.520 58.870 1.066 941.924
> 32768 17.767 17.208 17.205 58.887 0.885 1884.399
> 16384 18.258 17.252 18.035 57.407 1.407 3674.059
>
> 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 17.993 18.307 18.718 55.850 0.902 0.873
> 33554432 19.554 18.485 17.902 54.988 1.993 1.718
> 16777216 18.829 18.236 18.748 55.052 0.785 3.441
> 8388608 21.152 19.065 18.738 52.257 2.745 6.532
> 4194304 19.131 19.703 17.850 54.288 2.268 13.572
> 2097152 19.093 19.152 19.509 53.196 0.504 26.598
> 1048576 19.371 18.775 18.804 53.953 0.772 53.953
> 524288 20.003 17.911 18.602 54.470 2.476 108.940
> 262144 19.182 19.460 18.476 53.809 1.183 215.236
> 131072 19.403 19.192 18.907 53.429 0.567 427.435
> 65536 19.502 19.656 18.599 53.219 1.309 851.509
> 32768 18.746 18.747 18.250 55.119 0.701 1763.817
> 16384 20.977 19.437 18.840 51.951 2.319 3324.862

The results look inconsistently with what you had previously (89.7
MB/s). How can you explain it?

I think, most likely, there was some confusion between the tested and
patched versions of the kernel or you forgot to apply the io_context
patch. Please recheck.

> Ronald.
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