Re: [Xen-devel] how can native driver response quickly for low FIFO device

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 25 May 2006, at 14:08, Dong, Eddie wrote:

> O, sorry for the confuse message. Here I mean the issue in native 
> device
> (e.x. dom0 UART), not HVM virtual UART.
> When hardware UART device receives a byte, it will send pirq to dom0,
> although dom0 is not blocking but it may not get scheduled in at
> instance. Say it needs to wait for another domain (domU or domVMX) to
> run out of time slice, say 10ms in default scheduler. Within this 10ms,
> the hardware UART may receive another tens of bytes before dom0 UART
> device driver can really read the data and copy to driver buffer. So in
> this case the hardware UART device will become "receiving data
> overwritten",  which means receiving data lose for us :-(
> Is there anybody ever tried to use ttyS0 succesfully when multiple
> domain is running on same LP?
There's a 128-byte receive buffer. Bytes are greedily taken from the 
UART FIFO in interrupt context and written to the software receive 
buffer. If overflow were a problem we could obviously quite easily make 
that receive buffer substantially larger.
 -- Keir


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel