Re: [Qemu-devel] [PATCH] ivshmem: use PIO for BAR0(Doorbell) instead of MMIO to reduce notification time

[Avi Kivity]

On 11/14/2011 05:56 AM, address@hidden wrote:
> From: Hongyong Zang <address@hidden>
>
> Ivshmem(nahanni) is a mechanism for sharing host memory with VMs running on 
> the same host. Currently, guest notifies qemu by reading or writing ivshmem 
> device's PCI MMIO BAR0(Doorbell).
>
> This patch, changes this PCI MMIO BAR0(Doorbell) to PIO. And we find guest 
> accesses PIO BAR 30% faster than MMIO BAR.
>  
>      CharDriverState **eventfd_chr;
>      CharDriverState *server_chr;
> -    MemoryRegion ivshmem_mmio;
> +    MemoryRegion ivshmem_pio;
>  
> -    pcibus_t mmio_addr;
> +    pcibus_t pio_addr;


This is a backwards incompatible change.  The way to accomplish this is
to add a new BAR which aliases the old one.  The new BAR should not be
visible on guests created with -M pc-1.0 and below.  Please also update
the spec so that driver authors can make use of the new feature.

-- 
error compiling committee.c: too many arguments to function