Rusty Russell wrote: > On Sun, 2007-06-17 at 17:25 +0300, Avi Kivity wrote: > >> Rusty Russell wrote: >> >>> + /* Set up for reply. */ >>> + vblk->sg[0].page = virt_to_page(&vbr->in_hdr); >>> + vblk->sg[0].offset = offset_in_page(&vbr->in_hdr); >>> + vblk->sg[0].length = sizeof(vbr->in_hdr); >>> + num = blk_rq_map_sg(q, vbr->req, vblk->sg+1); >>> + vbr->out_hdr.id = vblk->vdev->ops->add_inbuf(vblk->vdev, vblk->sg, >>> + 1+num, vbr); >>> + if (IS_ERR_VALUE(vbr->out_hdr.id)) >>> + goto full; >>> + >>> + vblk->sg[0].page = virt_to_page(&vbr->out_hdr); >>> + vblk->sg[0].offset = offset_in_page(&vbr->out_hdr); >>> + vblk->sg[0].length = sizeof(vbr->out_hdr); >>> + >>> + vbr->out_id = vblk->vdev->ops->add_outbuf(vblk->vdev, vblk->sg, 1, >>> + vbr); >>> >> This strikes me as wasteful. Why not set up a single descriptor which >> contains both placement and the data itself? >> > > We could actually do this for write, but not for read (where the length > & sector need to be sent to other end, and the data comes from other > end). > >
So you map the first sg entry for output, and the rest for input. Less pretty, but more efficient. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
