2009/6/29 Wu Fengguang <fengguang.wu@xxxxxxxxx>: > On Sat, Jun 20, 2009 at 08:29:31PM +0800, Vladislav Bolkhovitin wrote: >> >> Wu Fengguang, on 06/20/2009 07:55 AM wrote: >> > On Fri, Jun 19, 2009 at 03:04:36AM +0800, Andrew Morton wrote: >> >> On Sun, 7 Jun 2009 06:45:38 +0800 >> >> Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote: >> >> >> >>>>> Do you have a place where the raw blktrace data can be retrieved for >> >>>>> more in-depth analysis? >> >>>> I think your comment is really adequate. In another thread, Wu Fengguang pointed >> >>>> out the same issue. >> >>>> I and Wu also wait his analysis. >> >>> And do it with a large readahead size :) >> >>> >> >>> Alan, this was my analysis: >> >>> >> >>> : Hifumi, can you help retest with some large readahead size? >> >>> : >> >>> : Your readahead size (128K) is smaller than your max_sectors_kb (256K), >> >>> : so two readahead IO requests get merged into one real IO, that means >> >>> : half of the readahead requests are delayed. >> >>> >> >>> ie. two readahead requests get merged and complete together, thus the effective >> >>> IO size is doubled but at the same time it becomes completely synchronous IO. >> >>> >> >>> : >> >>> : The IO completion size goes down from 512 to 256 sectors: >> >>> : >> >>> : before patch: >> >>> : 8,0 3 177955 50.050313976 0 C R 8724991 + 512 [0] >> >>> : 8,0 3 177966 50.053380250 0 C R 8725503 + 512 [0] >> >>> : 8,0 3 177977 50.056970395 0 C R 8726015 + 512 [0] >> >>> : 8,0 3 177988 50.060326743 0 C R 8726527 + 512 [0] >> >>> : 8,0 3 177999 50.063922341 0 C R 8727039 + 512 [0] >> >>> : >> >>> : after patch: >> >>> : 8,0 3 257297 50.000760847 0 C R 9480703 + 256 [0] >> >>> : 8,0 3 257306 50.003034240 0 C R 9480959 + 256 [0] >> >>> : 8,0 3 257307 50.003076338 0 C R 9481215 + 256 [0] >> >>> : 8,0 3 257323 50.004774693 0 C R 9481471 + 256 [0] >> >>> : 8,0 3 257332 50.006865854 0 C R 9481727 + 256 [0] >> >>> >> >> I haven't sent readahead-add-blk_run_backing_dev.patch in to Linus yet >> >> and it's looking like 2.6.32 material, if ever. >> >> >> >> If it turns out to be wonderful, we could always ask the -stable >> >> maintainers to put it in 2.6.x.y I guess. >> > >> > Agreed. The expected (and interesting) test on a properly configured >> > HW RAID has not happened yet, hence the theory remains unsupported. >> >> Hmm, do you see anything improper in the Ronald's setup (see >> http://sourceforge.net/mailarchive/forum.php?thread_name=a0272b440906030714g67eabc5k8f847fb1e538cc62%40mail.gmail.com&forum_name=scst-devel)? >> It is HW RAID based. > > No. Ronald's HW RAID performance is reasonably good. I meant Hifumi's > RAID performance is too bad and may be improved by increasing the > readahead size, hehe. > >> As I already wrote, we can ask Ronald to perform any needed tests. > > Thanks! Ronald's test results are: > > 231 MB/s HW RAID > 69.6 MB/s HW RAID + SCST > 89.7 MB/s HW RAID + SCST + this patch > > So this patch seem to help SCST, but again it would be better to > improve the SCST throughput first - it is now quite sub-optimal. > (Sorry for the long delay: currently I have not got an idea on > how to measure such timing issues.) > > And if Ronald could provide the HW RAID performance with this patch, > then we can confirm if this patch really makes a difference for RAID. I just tested raw HW RAID throughput with the patch applied, same readahead setting (512KB), and it doesn't look promising: ./blockdev-perftest -d -r /dev/cciss/c0d0 blocksize W W W R R R 67108864 -1 -1 -1 5.59686 5.4098 5.45396 33554432 -1 -1 -1 6.18616 6.13232 5.96124 16777216 -1 -1 -1 7.6757 7.32139 7.4966 8388608 -1 -1 -1 8.82793 9.02057 9.01055 4194304 -1 -1 -1 12.2289 12.6804 12.19 2097152 -1 -1 -1 13.3012 13.706 14.7542 1048576 -1 -1 -1 11.7577 12.3609 11.9507 524288 -1 -1 -1 12.4112 12.2383 11.9105 262144 -1 -1 -1 7.30687 7.4417 7.38246 131072 -1 -1 -1 7.95752 7.95053 8.60796 65536 -1 -1 -1 10.1282 10.1286 10.1956 32768 -1 -1 -1 9.91857 9.98597 10.8421 16384 -1 -1 -1 10.8267 10.8899 10.8718 8192 -1 -1 -1 12.0345 12.5275 12.005 4096 -1 -1 -1 15.1537 15.0771 15.1753 2048 -1 -1 -1 25.432 24.8985 25.4303 1024 -1 -1 -1 45.2674 45.2707 45.3504 512 -1 -1 -1 87.9405 88.5047 87.4726 It dropped down to 189 MB/s. :( Ronald. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
