Re: [linux-audio-dev] Re: [announce] [patch] Voluntary Kernel Preemption Patch

From: Lee Revell (rlrevell_at_joe-job.com)
Date: 07/14/04

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    To: Andrew Morton <akpm@osdl.org>
    Date:	Tue, 13 Jul 2004 18:32:41 -0400
    
    

    On Tue, 2004-07-13 at 05:29, Andrew Morton wrote:
    > Lee Revell <rlrevell@joe-job.com> wrote:
    > >
    > > On Tue, 2004-07-13 at 05:00, Andrew Morton wrote:
    > > > Lee Revell <rlrevell@joe-job.com> wrote:
    > > > >
    > > > > > framebuffer scrolling inside lock_kernel(). Tricky. Suggest you use X or
    > > > > > vgacon. You can try removing the lock_kernel() calls from do_tty_write(),
    > > > > > but make sure you're wearing ear protection.
    > > > > >
    > > > >
    > > > > OK, I figured this was not an easy one. I can just not do that.
    > > >
    > > > Why not? You can certainly try removing those [un]lock_kernel() calls.
    > > >
    > >
    > > Maybe I missed something. What exactly do you mean by 'make sure you're
    > > wearing ear protection'?
    > >
    >
    > It might go boom. If it does screw up, it probably won't be very seriously
    > bad - maybe some display glitches. Just an experiment.
    > -
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    >

    Seems to work perfectly. No visible display glitches.

    I would imagine that putting a modem on a tty, then stressing the system
    and watching for line errors would be a definitive test.

    --- drivers/char/tty_io.c.orig 2004-07-13 16:55:28.000000000 -0400
    +++ drivers/char/tty_io.c 2004-07-13 16:55:51.000000000 -0400
    @@ -684,17 +684,13 @@
                    return -ERESTARTSYS;
            }
            if ( test_bit(TTY_NO_WRITE_SPLIT, &tty->flags) ) {
    - lock_kernel();
                    written = write(tty, file, buf, count);
    - unlock_kernel();
            } else {
                    for (;;) {
                            unsigned long size = max((unsigned long)PAGE_SIZE*2, 16384UL);
                            if (size > count)
                                    size = count;
    - lock_kernel();
                            ret = write(tty, file, buf, size);
    - unlock_kernel();
                            if (ret <= 0)
                                    break;
                            written += ret;

    Lee

    -
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