Re: [Qemu-devel] Re: 2.6.24 says "serial8250: too much work for irq4" a lot.

[Blue Swirl]

On 2/9/08, H. Peter Anvin <address@hidden> wrote:
> Blue Swirl wrote:
> > On 2/9/08, Rob Landley <address@hidden> wrote:
> >> Here's a patch Peter Anvin wrote so the serial I/O doesn't flood the 
> >> kernel.
> >
> > The patch looks OK, but the throttling should benefit all devices, as
> > discussed here:
> > http://lists.gnu.org/archive/html/qemu-devel/2007-12/msg00283.html
>
> I strongly disagree with the sentiments in that post.
>
> This is not a matter of rate throttling, but simulated FIFO exhaustion
> -- they are NOT the same thing.  Simulated FIFO exhaustion is
> functionally equivalent to making sure there are interrupt windows
> opened in an otherwise-too-long critical section; it doesn't constrain
> any particular flow rate, as it still permits another interrupt to
> immediately come in.
>
> If you look at the patch, there are no timing dependencies; the only
> parameter is the depth of the virtual queue.  The exhaustion is
> completely controlled by target OS access patterns.

Thanks, this clarified the difference. But I'll rephrase my original comment:

The patch looks OK, but the simulated FIFO exhaustion should benefit
all devices, as
discussed here:
http://lists.gnu.org/archive/html/qemu-devel/2007-12/msg00283.html