From mboxrd@z Thu Jan 1 00:00:00 1970 From: Or Gerlitz Subject: Re: ib_ipoib: CSUM support in connected mode Date: Tue, 16 Sep 2014 09:47:43 +0300 Message-ID: <5417DD0F.9090201@mellanox.com> References: <20140914184621.GA4283@yuval-lab> <20140915185557.GA17422@yuval-lab> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140915185557.GA17422@yuval-lab> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Yuval Shaia Cc: Or Gerlitz , "linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" List-Id: linux-rdma@vger.kernel.org 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 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. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html