[ofa-general] [RFC] IPoIB UD 4K MTU support

[Dotan Barak]

Shirley Ma wrote:
> Hello Roland,
>
> 	IPoIB UD currently supports up to 2K MTU. Below is the draft patch to
> enable IPoIB UD 4K MTU support for any IB device who has 4K MTU like IBM
> eHCA. This patch limits packet in one page range by setting IPoIB UD MTU
> size as 4K-48 (40 GRH, 4 IPoIB header, 4 padding to IP header align) to
> avoid two contiguous pages allocation when kernel page size is 4K.
> Enabling IPoIB UD 4K MTU relies on both SM to set default broadcast
> group 4K MTU and of course switch should support 4K MTU. When SM default
> broadcast group MTU sets 2K, IPoIB UD MTU will fall back to 2K.
>
> 	I have tested 2K MTU. 4K MTU is still under testing. The reason I send
> this patch out before my test for review is I want comments as early as
> possible. So I can integrate the comments into this patch and hopefully
> we can make it into OFED-1.3-rc3 which is around Jan.30.
>
>   
Hi.
> +	if (!ib_query_port(hca, port, &attr))
> +		priv->max_ib_mtu = ib_mtu_enum_to_int(attr.);
> +	else {
> +		printk(KERN_WARNING "%s: ib_query_port %d failed\n", 
> +		       hca->name, port);
> +		goto device_init_failed;
> +	}
>   
What will happen if the IB port supports 4KB MTU but the operational MTU 
of this port is bellow this value?

thanks
Dotan