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97 lines
3.3 KiB
Diff
97 lines
3.3 KiB
Diff
From 9208d2863ac689a563b92f2161d8d1e7127d0add Mon Sep 17 00:00:00 2001
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From: Ilya Ponetayev <i.ponetaev@ndmsystems.com>
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Date: Thu, 25 Jun 2020 22:12:07 +0200
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Subject: [PATCH] sch_cake: don't try to reallocate or unshare skb
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unconditionally
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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cake_handle_diffserv() tries to linearize mac and network header parts of
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skb and to make it writable unconditionally. In some cases it leads to full
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skb reallocation, which reduces throughput and increases CPU load. Some
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measurements of IPv4 forward + NAPT on MIPS router with 580 MHz single-core
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CPU was conducted. It appears that on kernel 4.9 skb_try_make_writable()
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reallocates skb, if skb was allocated in ethernet driver via so-called
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'build skb' method from page cache (it was discovered by strange increase
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of kmalloc-2048 slab at first).
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Obtain DSCP value via read-only skb_header_pointer() call, and leave
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linearization only for DSCP bleaching or ECN CE setting. And, as an
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additional optimisation, skip diffserv parsing entirely if it is not needed
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by the current configuration.
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Fixes: c87b4ecdbe8d ("sch_cake: Make sure we can write the IP header before changing DSCP bits")
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Signed-off-by: Ilya Ponetayev <i.ponetaev@ndmsystems.com>
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[ fix a few style issues, reflow commit message ]
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Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
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Signed-off-by: David S. Miller <davem@davemloft.net>
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Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
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---
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net/sched/sch_cake.c | 41 ++++++++++++++++++++++++++++++-----------
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1 file changed, 30 insertions(+), 11 deletions(-)
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--- a/net/sched/sch_cake.c
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+++ b/net/sched/sch_cake.c
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@@ -1553,30 +1553,49 @@ static unsigned int cake_drop(struct Qdi
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static u8 cake_handle_diffserv(struct sk_buff *skb, u16 wash)
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{
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- int wlen = skb_network_offset(skb);
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+ const int offset = skb_network_offset(skb);
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+ u16 *buf, buf_;
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u8 dscp;
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switch (tc_skb_protocol(skb)) {
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case htons(ETH_P_IP):
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- wlen += sizeof(struct iphdr);
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- if (!pskb_may_pull(skb, wlen) ||
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- skb_try_make_writable(skb, wlen))
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+ buf = skb_header_pointer(skb, offset, sizeof(buf_), &buf_);
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+ if (unlikely(!buf))
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return 0;
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- dscp = ipv4_get_dsfield(ip_hdr(skb)) >> 2;
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- if (wash && dscp)
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+ /* ToS is in the second byte of iphdr */
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+ dscp = ipv4_get_dsfield((struct iphdr *)buf) >> 2;
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+
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+ if (wash && dscp) {
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+ const int wlen = offset + sizeof(struct iphdr);
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+
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+ if (!pskb_may_pull(skb, wlen) ||
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+ skb_try_make_writable(skb, wlen))
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+ return 0;
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+
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ipv4_change_dsfield(ip_hdr(skb), INET_ECN_MASK, 0);
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+ }
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+
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return dscp;
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case htons(ETH_P_IPV6):
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- wlen += sizeof(struct ipv6hdr);
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- if (!pskb_may_pull(skb, wlen) ||
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- skb_try_make_writable(skb, wlen))
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+ buf = skb_header_pointer(skb, offset, sizeof(buf_), &buf_);
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+ if (unlikely(!buf))
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return 0;
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- dscp = ipv6_get_dsfield(ipv6_hdr(skb)) >> 2;
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- if (wash && dscp)
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+ /* Traffic class is in the first and second bytes of ipv6hdr */
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+ dscp = ipv6_get_dsfield((struct ipv6hdr *)buf) >> 2;
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+
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+ if (wash && dscp) {
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+ const int wlen = offset + sizeof(struct ipv6hdr);
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+
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+ if (!pskb_may_pull(skb, wlen) ||
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+ skb_try_make_writable(skb, wlen))
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+ return 0;
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+
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ipv6_change_dsfield(ipv6_hdr(skb), INET_ECN_MASK, 0);
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+ }
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+
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return dscp;
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case htons(ETH_P_ARP):
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