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    SubjectRe: Linux 2.6.17-rc2
    On Fri, Apr 21 2006, Nick Piggin wrote:
    > Linh Dang wrote:
    > >Jens Axboe <axboe@suse.de> wrote:
    >
    > >>DVD burning probably isn't a good splice fit, since you need to do
    > >>more than actually just point the device at the data. SG_IO is
    > >>already zero-copy as it maps the user data into the kernel without
    > >>copying, so there's very little room for improvement there to begin
    > >>with.
    > >
    > >
    > >DVD burning on linux is mostly:
    > >
    > > mkisofs .... | growisofs ....
    > >
    > >Ideally, on mkisofs side, we'd be able to:
    > >
    > > - write some data/padding into the pipe
    > > - splice a HUGE file into the pipe
    > > - write some data/padding into the pipe
    > > - splice a HUGE file into the pipe
    > > ...
    > >
    > >On growisofs side, we'd be able to:
    > >
    > > - send some commands
    > > - splice N MBs of data from the pipe to the driver
    > > - send some commands
    > > - splice M MBs of data from the pipe to the driver
    > > ...
    > >
    > >What'd be nice is an ioctl to change the size of the pipe between
    > >mkisofs and growisofs.
    >
    > I don't see why the pipe buffers would be a problem though. It isn't
    > like you've lost any of the pagecache buffering (eg. from readahead)
    > or the application level buffering.

    Yes, hence the reason that a larger pipe / dynamic pipe wasn't even
    attempted yet. In the tests I did, manually increasing the pipe size
    yielded no noticable benefits.

    Conceptually it might be simpler for the mkisofs side to accept larger
    in-kernel pipes, but on the performance side I doubt it would matter a
    lot. The growisofs side sending data to the drive is not limited by the
    64k pipe, typically the commands will be smaller than that anyways. So
    "splice N MBs of data from the pipe to the driver" is a nice dream, but
    that's not how you talk to the device anyways.

    --
    Jens Axboe

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