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Date: Sun, 28 Sep 2014 11:07:16 -0700 From: Alexei Starovoitov <ast@...mgrid.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: Or Gerlitz <gerlitz.or@...il.com>, "David S. Miller" <davem@...emloft.net>, Jesper Dangaard Brouer <brouer@...hat.com>, Eric Dumazet <edumazet@...gle.com>, John Fastabend <john.r.fastabend@...el.com>, Linux Netdev List <netdev@...r.kernel.org>, Amir Vadai <amirv@...lanox.com>, Or Gerlitz <or.gerlitz@...il.com> Subject: Re: [PATCH net-next] mlx4: optimize xmit path On Sat, Sep 27, 2014 at 3:56 PM, Eric Dumazet <eric.dumazet@...il.com> wrote: > From: Eric Dumazet <edumazet@...gle.com> > > First I implemented skb->xmit_more support, and pktgen throughput > went from ~5Mpps to ~10Mpps. > > Then, looking closely at this driver I found false sharing problems that > should be addressed by this patch, as my pktgen now reaches 14.7 Mpps > on a single TX queue, with a burst factor of 8. > > So this patch in a whole permits to improve raw performance on a single > TX queue from about 5 Mpps to 14.7 Mpps. this is great improvement! Thank you for leading this effort. 10G line rate is definitely nice :) Hopefully Or can demo similar numbers with 40G nic as well :) > + if (ring->bf_enabled && desc_size <= MAX_BF && !bounce && > + !vlan_tx_tag_present(skb) && send_doorbell) { feels something wrong here, since it checks for send_doorbell, but iowrite() happens in the 'else' part of this branch with another 'if (send_doorbell)' The previous code seems equally confusing to me. > + tx_desc->ctrl.bf_qpn = ring->doorbell_qpn | > + cpu_to_be32(real_size); > > op_own |= htonl((bf_index & 0xffff) << 8); > - /* Ensure new descirptor hits memory > - * before setting ownership of this descriptor to HW */ > + /* Ensure new descriptor hits memory > + * before setting ownership of this descriptor to HW > + */ > wmb(); > tx_desc->ctrl.owner_opcode = op_own; > > wmb(); > > - mlx4_bf_copy(ring->bf.reg + ring->bf.offset, (unsigned long *) &tx_desc->ctrl, > - desc_size); > + mlx4_bf_copy(ring->bf.reg + ring->bf.offset, > + &tx_desc->ctrl, > + desc_size); > > wmb(); > > ring->bf.offset ^= ring->bf.buf_size; > } else { > - /* Ensure new descirptor hits memory > - * before setting ownership of this descriptor to HW */ > + tx_desc->ctrl.vlan_tag = cpu_to_be16(vlan_tag); > + tx_desc->ctrl.ins_vlan = MLX4_WQE_CTRL_INS_VLAN * > + !!vlan_tx_tag_present(skb); > + tx_desc->ctrl.fence_size = real_size; > + > + /* Ensure new descriptor hits memory > + * before setting ownership of this descriptor to HW > + */ > wmb(); > tx_desc->ctrl.owner_opcode = op_own; > - wmb(); > - iowrite32be(ring->doorbell_qpn, ring->bf.uar->map + MLX4_SEND_DOORBELL); > + > + if (send_doorbell) { > + wmb(); /* ensure owner_opcode is written */ > + iowrite32(ring->doorbell_qpn, > + ring->bf.uar->map + MLX4_SEND_DOORBELL); > + } shinfo, prefetch and access_once additions all look useful to me. Thanks! -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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