Re: [Qemu-devel] [PATCH 0/2] ide: convert pio code path to asynchronous I/O

[Paolo Bonzini <pbonzini@redhat.com>]

Il 28/03/2012 17:43, Stefan Hajnoczi ha scritto:
> IDE PIO mode is currently implemented using synchronous I/O functions.  There's
> no need to do this because the IDE interface is actually designed with polling
> and interrupts in mind - we can do asynchronous I/O and let the guest know when
> the operation has completed.  The benefit of asynchronous I/O is that the guest
> can continue executing code and is more responsive.
> 
> The second aim of this conversion is to avoid calling bdrv_read()/bdrv_write()
> since they do not work with I/O throttling.  This means guests should now boot
> IDE drives successfully when I/O throttling is enabled.
> 
> Note that ATAPI is not converted yet and still uses bdrv_read() in two
> locations.  A future patch will have to convert ATAPI so CD-ROMs also do
> asynchronous I/O.
> 
> I have tested both Windows 7 Home Premium and Red Hat Enterprise Linux 6.0
> guests with these patches.  In Windows, use the device manager to disable DMA
> on the IDE channels.  Under recent Linux kernels, use the libata.dma=0 kernel
> parameter.
> 
> Chris and Richard: Please test this to confirm that it fixes the hang you
> reported.
> 
> Stefan Hajnoczi (2):
>   ide: convert ide_sector_read() to asynchronous I/O
>   ide: convert ide_sector_write() to asynchronous I/O
> 
>  hw/ide/core.c     |  129 ++++++++++++++++++++++++++++++++++++----------------
>  hw/ide/internal.h |    2 +
>  2 files changed, 91 insertions(+), 40 deletions(-)
> 

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Paolo