On 9/15/2014 9:55 PM, Yuval Shaia wrote:
On Mon, Sep 15, 2014 at 05:47:19PM +0300, Or Gerlitz wrote:
>On Sun, Sep 14, 2014 at 9:46 PM, Yuval Shaia<yuval.shaia@xxxxxxxxxx> wrote:
>>By default, IPoIB-CM driver uses 64k MTU. Larger MTU gives better performance.
>>This MTU plus overhead puts the memory allocation for IP based packets at 32 4k pages (order 5),
>So if we make sure that the advertized netdevice MTU is 64K minus that
>over head we're back to order four
>allocation and problem is solved? note that RFC 4755 makes sure that
>the MTU is negotiated in both directions,
>so it can have any value, specifically 64K - that epsilon which will
>hopefully make you happy
Interesting point. But please note that in any case, when not using scatter/gather we force the allocation of large contiguous physical memory.
On the post you wrote "[...] resolve the issue by removing the physically contiguous memory requirement using Scatter/Gather feature that exists in Linux".
I assume you refer to NETIF_F_SG, right? so your claim is that Linux will not effectively use the driver ability to serve SG skbs unless the driver also advertizes (say) NETIF_F_IP_CSUM?!
I thought it's the other way around -- that is supporting checksum offloading is useless unless SG is supported. Can you provide pointer into the network stack code/documentation that supports your claim?
Or.
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