Re: [Qemu-devel] [PATCH] honor IDE_DMA_BUF_SECTORS

[Avi Kivity]

Stefano Stabellini wrote:
> Unfortunately that is not really helpful: after the split done by
> cpu_physical_memory_map the iovector is converted in a buffer in
> bdrv_aio_rw_vector and then the full length of the buffer is passed on
> to the bdrv_aio_write\read for the dma operation.
>
> I need a way to set a maximum limit for the total number of sectors in
> the dma operation, much like blk_queue_max_phys_segments in the kernel.
>
> This could also be useful to make sure that we don't allocate bounce
> buffers bigger than a predetermined limit.
>   

If cpu_physical_memory_map() returns NULL, then dma-helpers.c will stop 
collecting sg entries and submit the I/O.  Tuning that will control how 
vectored requests are submitted.

If you problem is specifically with the bdrv_aio_rw_vector bounce 
buffer, then note that this is a temporary measure until vectored aio is 
in place, through preadv/pwritev and/or linux-aio IO_CMD_PREADV.  You 
should either convert to that when it is merged, or implement request 
splitting in bdrv_aio_rw_vector.

Can you explain your problem in more detail?

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