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

[H. Peter Anvin]

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.

        -hpa