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

Ronald Moesbergen
2009-07-07T06:49:33Z

2009/7/6 Vladislav Bolkhovitin <vst@vlnb.net>:
> Ronald Moesbergen, on 07/06/2009 06:37 PM wrote:
>>
>> 2009/7/6 Vladislav Bolkhovitin <vst@vlnb.net>:
>>>
>>> (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 had more patches applied with that test: (scst_exec_req_fifo-2.6.29,
>> put_page_callback-2.6.29) and I used a different dd command:
>>
>> dd if=/dev/sdc of=/dev/zero bs=512K count=2000
>>
>> But all that said, I can't reproduce speeds that high now. Must have
>> made a mistake back then (maybe I forgot to clear the pagecache).
>
> If you forgot to clear the cache, you would had had the wire throughput (110
> MB/s) or more.

Maybe. Maybe just part of what I was transferring was in cache. I had
done some tests on the filesystem on that same block device too.

>>> 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.
>>
>> The tests above were definitely done right, I just rechecked the
>> patches, and I do see an average increase of about 10MB/s over an
>> unpatched kernel. But overall the performance is still pretty bad.
>
> Have you rebuild and reinstall SCST after patching kernel?

Yes I have. And the warning about missing io_context patches wasn't
there during the compilation.

Ronald.