Linux Virtualization - May 2019 - [PATCH v2 7/8] vsock/virtio: increase RX buffer size to 64 KiB

On 2019/5/10 ??8:58, Stefano Garzarella wrote:
> In order to increase host -> guest throughput with large packets,
> we can use 64 KiB RX buffers.
>
> Signed-off-by: Stefano Garzarella <sgarzare at redhat.com>
> ---
>   include/linux/virtio_vsock.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index 84b72026d327..5a9d25be72df 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -10,7 +10,7 @@
>   #define VIRTIO_VSOCK_DEFAULT_MIN_BUF_SIZE	128
>   #define VIRTIO_VSOCK_DEFAULT_BUF_SIZE		(1024 * 256)
>   #define VIRTIO_VSOCK_DEFAULT_MAX_BUF_SIZE	(1024 * 256)
> -#define VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE	(1024 * 4)
> +#define VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE	(1024 * 64)
>   #define VIRTIO_VSOCK_MAX_BUF_SIZE		0xFFFFFFFFUL
>   #define VIRTIO_VSOCK_MAX_PKT_BUF_SIZE		(1024 * 64)
>   

We probably don't want such high order allocation. It's better to switch
to use order 0 pages in this case. See add_recvbuf_big() for virtio-net. 
If we get datapath unified, we will get more stuffs set.

Thanks

On Mon, May 13, 2019 at 06:01:52PM +0800, Jason Wang
wrote:
> 
> On 2019/5/10 ??8:58, Stefano Garzarella wrote:
> > In order to increase host -> guest throughput with large packets,
> > we can use 64 KiB RX buffers.
> > 
> > Signed-off-by: Stefano Garzarella <sgarzare at redhat.com>
> > ---
> >   include/linux/virtio_vsock.h | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/virtio_vsock.h
b/include/linux/virtio_vsock.h
> > index 84b72026d327..5a9d25be72df 100644
> > --- a/include/linux/virtio_vsock.h
> > +++ b/include/linux/virtio_vsock.h
> > @@ -10,7 +10,7 @@
> >   #define VIRTIO_VSOCK_DEFAULT_MIN_BUF_SIZE	128
> >   #define VIRTIO_VSOCK_DEFAULT_BUF_SIZE		(1024 * 256)
> >   #define VIRTIO_VSOCK_DEFAULT_MAX_BUF_SIZE	(1024 * 256)
> > -#define VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE	(1024 * 4)
> > +#define VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE	(1024 * 64)
> >   #define VIRTIO_VSOCK_MAX_BUF_SIZE		0xFFFFFFFFUL
> >   #define VIRTIO_VSOCK_MAX_PKT_BUF_SIZE		(1024 * 64)
> 
> 
> We probably don't want such high order allocation. It's better to
switch to
> use order 0 pages in this case. See add_recvbuf_big() for virtio-net. If we
> get datapath unified, we will get more stuffs set.
IIUC, you are suggesting to allocate only pages and put them in a
scatterlist, then add them to the virtqueue.

Is it correct?

The issue that I have here, is that the virtio-vsock guest driver, see
virtio_vsock_rx_fill(), allocates a struct virtio_vsock_pkt that
contains the room for the header, then allocates the buffer for the payload.
At this point it fills the scatterlist with the &virtio_vsock_pkt.hdr and
the
buffer for the payload.

Changing this will require several modifications, and if we get datapath
unified, I'm not sure it's worth it.
Of course, if we leave the datapaths separated, I'd like to do that later.

What do you think?

Thanks,
Stefano

On 2019/5/14 ??1:51, Stefano Garzarella wrote:
> On Mon, May 13, 2019 at 06:01:52PM +0800, Jason Wang wrote:
>> On 2019/5/10 ??8:58, Stefano Garzarella wrote:
>>> In order to increase host -> guest throughput with large
packets,
>>> we can use 64 KiB RX buffers.
>>>
>>> Signed-off-by: Stefano Garzarella <sgarzare at redhat.com>
>>> ---
>>>    include/linux/virtio_vsock.h | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/include/linux/virtio_vsock.h
b/include/linux/virtio_vsock.h
>>> index 84b72026d327..5a9d25be72df 100644
>>> --- a/include/linux/virtio_vsock.h
>>> +++ b/include/linux/virtio_vsock.h
>>> @@ -10,7 +10,7 @@
>>>    #define VIRTIO_VSOCK_DEFAULT_MIN_BUF_SIZE	128
>>>    #define VIRTIO_VSOCK_DEFAULT_BUF_SIZE		(1024 * 256)
>>>    #define VIRTIO_VSOCK_DEFAULT_MAX_BUF_SIZE	(1024 * 256)
>>> -#define VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE	(1024 * 4)
>>> +#define VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE	(1024 * 64)
>>>    #define VIRTIO_VSOCK_MAX_BUF_SIZE		0xFFFFFFFFUL
>>>    #define VIRTIO_VSOCK_MAX_PKT_BUF_SIZE		(1024 * 64)
>>
>> We probably don't want such high order allocation. It's better
to switch to
>> use order 0 pages in this case. See add_recvbuf_big() for virtio-net.
If we
>> get datapath unified, we will get more stuffs set.
> IIUC, you are suggesting to allocate only pages and put them in a
> scatterlist, then add them to the virtqueue.
>
> Is it correct?

Yes since you are using:

 ??????????????? pkt->buf = kmalloc(buf_len, GFP_KERNEL);
 ??????????????? if (!pkt->buf) {
 ??????????????????????? virtio_transport_free_pkt(pkt);
 ??????????????????????? break;
 ??????????????? }

This is likely to fail when the memory is fragmented which is kind of 
fragile.

>
> The issue that I have here, is that the virtio-vsock guest driver, see
> virtio_vsock_rx_fill(), allocates a struct virtio_vsock_pkt that
> contains the room for the header, then allocates the buffer for the
payload.
> At this point it fills the scatterlist with the &virtio_vsock_pkt.hdr
and the
> buffer for the payload.

This part should be fine since what is needed is just adding more pages 
to sg[] and call virtuqeueu_add_sg().

>
> Changing this will require several modifications, and if we get datapath
> unified, I'm not sure it's worth it.
> Of course, if we leave the datapaths separated, I'd like to do that
later.
>
> What do you think?

For the driver it self, it should not be hard. But I think you mean the 
issue of e.g virtio_vsock_pkt itself which doesn't support sg. For short 
time, maybe we can use kvec instead.

Thanks

>
> Thanks,
> Stefano