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    SubjectRe: dm-ioband + bio-cgroup benchmarks
    On Fri, Sep 19, 2008 at 03:12:21PM +0900, Hirokazu Takahashi wrote:
    > Hi,
    >
    > > > Hi All,
    > > >
    > > > I have got excellent results of dm-ioband, that controls the disk I/O
    > > > bandwidth even when it accepts delayed write requests.
    > > >
    > > > In this time, I ran some benchmarks with a high-end storage. The
    > > > reason was to avoid a performance bottleneck due to mechanical factors
    > > > such as seek time.
    > > >
    > > > You can see the details of the benchmarks at:
    > > > http://people.valinux.co.jp/~ryov/dm-ioband/hps/
    > > >
    > >
    > > Hi Ryo,
    > >
    > > I had a query about dm-ioband patches. IIUC, dm-ioband patches will break
    > > the notion of process priority in CFQ because now dm-ioband device will
    > > hold the bio and issue these to lower layers later based on which bio's
    > > become ready. Hence actual bio submitting context might be different and
    > > because cfq derives the io_context from current task, it will be broken.
    >
    > This is completely another problem we have to solve.
    > The CFQ scheduler has really bad assumption that the current process
    > must be the owner. This problem occurs when you use some of device
    > mapper devices or use linux aio.
    >
    > > To mitigate that problem, we probably need to implement Fernando's
    > > suggestion of putting io_context pointer in bio.
    > >
    > > Have you already done something to solve this issue?
    >
    > Actually, I already have a patch to solve this problem, which make
    > each bio have a pointer to the io_context of the owner process.
    > Would you take a look at the thread whose subject is "I/O context
    > inheritance" in:
    > http://www.uwsg.iu.edu/hypermail/linux/kernel/0804.2/index.html#2850
    >
    > Fernando also knows this.

    Great. Sure I will have a look at this thread. This is something we shall
    have to implement, irrespective of the fact whether we go for dm-ioband
    approach or an rb-tree per request queue approach.

    Thanks
    Vivek


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