| Message ID | 1415184622-19421-1-git-send-email-david.vrabel@citrix.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On Wed, 2014-11-05 at 10:50 +0000, David Vrabel wrote: > From: Malcolm Crossley <malcolm.crossley@citrix.com> > > Unconditionally pulling 128 bytes into the linear area is not required > for: > > - security: Every protocol demux starts with pskb_may_pull() to pull > frag data into the linear area, if necessary, before looking at > headers. > > - performance: Netback has already grant copied up-to 128 bytes from > the first slot of a packet into the linear area. The first slot > normally contain all the IPv4/IPv6 and TCP/UDP headers. Thanks for adding these. > The unconditional pull would often copy frag data unnecessarily. This > is a performance problem when running on a version of Xen where grant > unmap avoids TLB flushes for pages which are not accessed. TLB > flushes can now be avoided for > 99% of unmaps (it was 0% before). > > Grant unmap TLB flush avoidance will be available in a future version > of Xen (probably 4.6). > > Signed-off-by: Malcolm Crossley <malcolm.crossley@citrix.com> > Signed-off-by: David Vrabel <david.vrabel@citrix.com> Acked-by: Ian Campbell <ian.campbell@citrix.com> -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: David Vrabel <david.vrabel@citrix.com> Date: Wed, 5 Nov 2014 10:50:22 +0000 > From: Malcolm Crossley <malcolm.crossley@citrix.com> > > Unconditionally pulling 128 bytes into the linear area is not required > for: > > - security: Every protocol demux starts with pskb_may_pull() to pull > frag data into the linear area, if necessary, before looking at > headers. > > - performance: Netback has already grant copied up-to 128 bytes from > the first slot of a packet into the linear area. The first slot > normally contain all the IPv4/IPv6 and TCP/UDP headers. > > The unconditional pull would often copy frag data unnecessarily. This > is a performance problem when running on a version of Xen where grant > unmap avoids TLB flushes for pages which are not accessed. TLB > flushes can now be avoided for > 99% of unmaps (it was 0% before). > > Grant unmap TLB flush avoidance will be available in a future version > of Xen (probably 4.6). > > Signed-off-by: Malcolm Crossley <malcolm.crossley@citrix.com> > Signed-off-by: David Vrabel <david.vrabel@citrix.com> Applied, thanks. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c index 730252c..14e18bb 100644 --- a/drivers/net/xen-netback/netback.c +++ b/drivers/net/xen-netback/netback.c @@ -82,6 +82,16 @@ MODULE_PARM_DESC(max_queues, static unsigned int fatal_skb_slots = FATAL_SKB_SLOTS_DEFAULT; module_param(fatal_skb_slots, uint, 0444); +/* The amount to copy out of the first guest Tx slot into the skb's + * linear area. If the first slot has more data, it will be mapped + * and put into the first frag. + * + * This is sized to avoid pulling headers from the frags for most + * TCP/IP packets. + */ +#define XEN_NETBACK_TX_COPY_LEN 128 + + static void xenvif_idx_release(struct xenvif_queue *queue, u16 pending_idx, u8 status); @@ -125,13 +135,6 @@ static inline struct xenvif_queue *ubuf_to_queue(const struct ubuf_info *ubuf) pending_tx_info[0]); } -/* This is a miniumum size for the linear area to avoid lots of - * calls to __pskb_pull_tail() as we set up checksum offsets. The - * value 128 was chosen as it covers all IPv4 and most likely - * IPv6 headers. - */ -#define PKT_PROT_LEN 128 - static u16 frag_get_pending_idx(skb_frag_t *frag) { return (u16)frag->page_offset; @@ -1446,9 +1449,9 @@ static void xenvif_tx_build_gops(struct xenvif_queue *queue, index = pending_index(queue->pending_cons); pending_idx = queue->pending_ring[index]; - data_len = (txreq.size > PKT_PROT_LEN && + data_len = (txreq.size > XEN_NETBACK_TX_COPY_LEN && ret < XEN_NETBK_LEGACY_SLOTS_MAX) ? - PKT_PROT_LEN : txreq.size; + XEN_NETBACK_TX_COPY_LEN : txreq.size; skb = xenvif_alloc_skb(data_len); if (unlikely(skb == NULL)) { @@ -1653,11 +1656,6 @@ static int xenvif_tx_submit(struct xenvif_queue *queue) } } - if (skb_is_nonlinear(skb) && skb_headlen(skb) < PKT_PROT_LEN) { - int target = min_t(int, skb->len, PKT_PROT_LEN); - __pskb_pull_tail(skb, target - skb_headlen(skb)); - } - skb->dev = queue->vif->dev; skb->protocol = eth_type_trans(skb, skb->dev); skb_reset_network_header(skb);