>-----Original Message----- >From: Herbert Xu [mailto:herbert@xxxxxxxxxxxxxxxxxxx] >Sent: Friday, June 18, 2010 1:59 PM >To: Xin, Xiaohui >Cc: Stephen Hemminger; netdev@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; >linux-kernel@xxxxxxxxxxxxxxx; mst@xxxxxxxxxx; mingo@xxxxxxx; davem@xxxxxxxxxxxxx; >jdike@xxxxxxxxxxxxxxx; Rusty Russell >Subject: Re: [RFC PATCH v7 01/19] Add a new structure for skb buffer from external. > >On Fri, Jun 18, 2010 at 01:26:49PM +0800, Xin, Xiaohui wrote: >> >> Herbert, >> I have questions about the idea above: >> 1) Since netdev_alloc_skb() is still there, and we only modify alloc_page(), >> then we don't need napi_gro_frags() any more, the driver's original receiving >> function is ok. Right? > >Well I was actually thinking about converting all drivers that >need this to napi_gro_frags. But now that you mention it, yes >we could still keep the old interface to minimise the work. > >> 2) Is napi_gro_frags() only suitable for TCP protocol packet? >> I have done a small test for ixgbe driver to let it only allocate paged buffers >> and found kernel hangs when napi_gro_frags() receives an ARP packet. > >It should work with any packet. In fact, I'm pretty sure the >other drivers (e.g., cxgb3) use that interface for all packets. > Thanks for the verification. By the way, does that mean that nearly all drivers can use the same napi_gro_frags() to receive buffers though currently each driver has it's own receiving function? >> 3) As I have mentioned above, with this idea, netdev_alloc_skb() will allocate >> as usual, the data pointed by skb->data will be copied into the first guest buffer. >> That means we should reserve sufficient room in guest buffer. For PS mode >> supported driver (for example ixgbe), the room will be more than 128. After 128bytes, >> we will put the first frag data. Look into virtio-net.c the function page_to_skb() >> and receive_mergeable(), that means we should modify guest virtio-net driver to >> compute the offset as the parameter for skb_set_frag(). >> >> How do you think about this? Attached is a patch to how to modify the guest driver. >> I reserve 512 bytes as an example, and transfer the header len of the skb in hdr->hdr_len. > >Expanding the buffer size to 512 bytes to accomodate PS mode >looks reasonable to me. > >However, I don't think we should increase the copy threshold to >512 bytes at the same time. I don't have any figures myself but >I think if we are to make such a change it should be a separate >one and come with supporting numbers. > Let me have a look to see if I can retain the copy threshold as 128 bytes and copy the header data safely. >Cheers, >-- >Visit Openswan at http://www.openswan.org/ >Email: Herbert Xu ~{PmV>HI~} <herbert@xxxxxxxxxxxxxxxxxxx> >Home Page: http://gondor.apana.org.au/~herbert/ >PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
