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    SubjectRe: [OT] ALSA userspace API complexity
    On Sun, Jan 08, 2006 at 10:42:02AM +0100, Jaroslav Kysela wrote:
    > On Sun, 8 Jan 2006, Olivier Galibert wrote:
    > > On Sat, Jan 07, 2006 at 03:32:27PM +0100, Takashi Iwai wrote:
    > > > Yes, it's a known problem to be fixed. But, it's no excuse to do
    > > > _everything_ in the kernel (which OSS requires).
    > >
    > > OSS does not require to do anything in the kernel except an entry
    > > point.
    > >
    > >
    > > > And if the application doesn't support, who and where converts it?
    > > > With OSS API, it's a job of the kernel.
    > >
    > > Once again no. Nothing prevents the kernel to forward the data to
    > > userland daemons depending on a userspace-uploaded configuration.
    > But it's quite ineffecient. The kernel must switch tasks at least twice
    > or more. It's the major problem with the current OSS API.

    Once. U->K or K->U is not task switching and accordingly has a very
    low cost. It's changing of userspace task that is costly. And dmix
    _is_ a task switch, there is no performance difference between talking
    with it through shared memory and semaphores and who knows what else
    and talking with it through a kernel interface.

    You should count how many U-U switches and U-K syscalls communicating
    with dmix represents. Hard to do for a simple user, since the
    protocol is not documented.


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