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. > > > > [...] The proposal is to tell to network stack that IPoIB-CM supports IP > > Checksum offload. This enables Linux IPoIB-CM driver to use Scatter/Gather feature. Network > > sends the IP packet without adding the IP Checksum to the header. > > AFAIK, on the TX side, Linux will always compute the IP checksum, but > with this suggestion, > not the TCP checksum which is assumed to be computed by the card... so > we will have a TCP > packet on the wire without checksum. And if this packet goes through > gateway it will be dropped at > some point, agree? Agree. This is why driver must expose interface to system administrator to disable/enable this feature according to his network topology. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
