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

[Lee Revell]

On Tue, 2004-07-13 at 05:29, Andrew Morton wrote:
> Lee Revell <rlrevell at joe-job.com> wrote:
> >
> > On Tue, 2004-07-13 at 05:00, Andrew Morton wrote:
> > > Lee Revell <rlrevell at 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