[Devel] Re: [PATCH 1/1] dm-ioband: I/O bandwidth controller

[Ryo Tsuruta]

Hi Vivek,

From: Ryo Tsuruta <ryov at valinux.co.jp>
Subject: [PATCH 1/1] dm-ioband: I/O bandwidth controller
Date: Tue, 19 May 2009 17:39:28 +0900 (JST)

> Hi Alasdair and all,
> 
> This is the dm-ioband version 1.11.0 release. This patch can be
> applied cleanly to current agk's tree. Alasdair, please give some
> comments and suggestions.
> 
> Changes from the previous release:
> - Classify IOs in sync/async instead of read/write since the IO
>   request allocation/congestion logic were changed to be sync/async
>   based.
> - IOs belong to the real-time class are dispatched in preference to
>   other IOs, regardless of the assigned bandwidth.

I ran your script from the following URL to see IOs belong to the
real-time class take precedence.
http://linux.derkeiler.com/Mailing-Lists/Kernel/2009-04/msg08355.html

    Script
    ======
    # /dev/mapper/ioband1 is mounted on /mnt1
    rm /mnt1/aggressivewriter
    sync
    echo 3 > /proc/sys/vm/drop_caches
    # launch an hostile writer
    ionice -c2 -n7 dd if=/dev/zero of=/mnt1/aggressivewriter \
       bs=4K count=524288 conv=fdatasync &
    # Reader
    ionice -c1 -n0 dd if=/mnt1/testzerofile1 of=/dev/null &
    wait $!
    echo "reader finished"

    old dm-ioband
    =============
    First run
    2147483648 bytes (2.1 GB) copied, 100.343 seconds, 21.4 MB/s (Reader)
    reader finished
    2147483648 bytes (2.1 GB) copied, 101.107 seconds, 21.2 MB/s (Writer)

    new dm-ioband v1.11.0
    =====================
    First run
    2147483648 bytes (2.1 GB) copied, 35.0623 seconds, 61.2 MB/s (Reader)
    reader finished
    2147483648 bytes (2.1 GB) copied, 87.6979 seconds, 24.5 MB/s (Writer)

The RT reader took precedence over the aggressive writer, regardless
of assigned bandwidth. However, I think that some sort of limitation
for RT IOs is needed. What do you think?

Thanks,
Ryo Tsuruta
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