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Date: Fri, 17 Jul 2009 22:23:36 +0400 From: Vladislav Bolkhovitin <vst@...b.net> To: Ronald Moesbergen <intercommit@...il.com> CC: fengguang.wu@...el.com, linux-kernel@...r.kernel.org, akpm@...ux-foundation.org, kosaki.motohiro@...fujitsu.com, Alan.Brunelle@...com, linux-fsdevel@...r.kernel.org, jens.axboe@...cle.com, randy.dunlap@...cle.com, Bart Van Assche <bart.vanassche@...il.com> Subject: Re: [RESEND] [PATCH] readahead:add blk_run_backing_dev Ronald Moesbergen, on 07/17/2009 06:15 PM wrote: > 2009/7/16 Vladislav Bolkhovitin <vst@...b.net>: >> Ronald Moesbergen, on 07/16/2009 11:32 AM wrote: >>> 2009/7/15 Vladislav Bolkhovitin <vst@...b.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? Thanks, Vlad -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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