Il 18/12/2012 14:36, Michael S. Tsirkin ha scritto:
> Some comments without arguing about whether the performance
> benefit is worth it.
>
> On Tue, Dec 18, 2012 at 01:32:48PM +0100, Paolo Bonzini wrote:
>> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
>> index cf8adb1..39d56c4 100644
>> --- a/include/linux/virtio.h
>> +++ b/include/linux/virtio.h
>> @@ -7,6 +7,7 @@
>> #include <linux/spinlock.h>
>> #include <linux/device.h>
>> #include <linux/mod_devicetable.h>
>> +#include <linux/dma-direction.h>
>> #include <linux/gfp.h>
>>
>> /**
>> @@ -40,6 +41,26 @@ int virtqueue_add_buf(struct virtqueue *vq,
>> void *data,
>> gfp_t gfp);
>>
>> +struct virtqueue_buf {
>> + struct virtqueue *vq;
>> + struct vring_desc *indirect, *tail;
>
> This is wrong: virtio.h does not include virito_ring.h,
> and it shouldn't by design depend on it.
>
>> + int head;
>> +};
>> +
>
> Can't we track state internally to the virtqueue?
> Exposing it seems to buy us nothing since you can't
> call add_buf between start and end anyway.
I wanted to keep the state for these functions separate from the rest.
I don't think it makes much sense to move it to struct virtqueue unless
virtqueue_add_buf is converted to use the new API (doesn't make much
sense, could even be a tad slower).
On the other hand moving it there would eliminate the dependency on
virtio_ring.h. Rusty, what do you think?
>> +int virtqueue_start_buf(struct virtqueue *_vq,
>> + struct virtqueue_buf *buf,
>> + void *data,
>> + unsigned int count,
>> + unsigned int count_sg,
>> + gfp_t gfp);
>> +
>> +void virtqueue_add_sg(struct virtqueue_buf *buf,
>> + struct scatterlist sgl[],
>> + unsigned int count,
>> + enum dma_data_direction dir);
>> +
>
> And idea: in practice virtio scsi seems to always call sg_init_one, no?
> So how about we pass in void* or something and avoid using sg and count?
> This would make it useful for -net BTW.
It also passes the scatterlist from the LLD. It calls sg_init_one for
the request/response headers.
Paolo
>> +void virtqueue_end_buf(struct virtqueue_buf *buf);
>> +
>> void virtqueue_kick(struct virtqueue *vq);
>>
>> bool virtqueue_kick_prepare(struct virtqueue *vq);
>> --
>> 1.7.1
>>
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