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

Vladislav Bolkhovitin
2009-07-20T07:20:48Z

Vladislav Bolkhovitin, on 07/17/2009 10:23 PM wrote:
> 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?

Case of 5 I/O threads (default) will also be interesting. I.e., overall,
cases of 1, 2 and 5 I/O threads with deadline scheduler on the server.

Thanks,
Vlad