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net: ipv6: seg6_iptunnel: mitigate 2-realloc issue
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This patch mitigates the two-reallocations issue with seg6_iptunnel by
providing the dst_entry (in the cache) to the first call to
skb_cow_head(). As a result, the very first iteration would still
trigger two reallocations (i.e., empty cache), while next iterations
would only trigger a single reallocation.

Performance tests before/after applying this patch, which clearly shows
the improvement:
- before: https://ibb.co/3Cg4sNH
- after: https://ibb.co/8rQ350r

Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
Cc: David Lebrun <dlebrun@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
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Justin Iurman authored and Paolo Abeni committed Dec 5, 2024
1 parent dce5251 commit 40475b6
Showing 1 changed file with 52 additions and 33 deletions.
85 changes: 52 additions & 33 deletions net/ipv6/seg6_iptunnel.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -124,8 +124,8 @@ static __be32 seg6_make_flowlabel(struct net *net, struct sk_buff *skb,
return flowlabel;
}

/* encapsulate an IPv6 packet within an outer IPv6 header with a given SRH */
int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, int proto)
static int __seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh,
int proto, struct dst_entry *cache_dst)
{
struct dst_entry *dst = skb_dst(skb);
struct net *net = dev_net(dst->dev);
Expand All @@ -137,7 +137,7 @@ int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, int proto)
hdrlen = (osrh->hdrlen + 1) << 3;
tot_len = hdrlen + sizeof(*hdr);

err = skb_cow_head(skb, tot_len + skb->mac_len);
err = skb_cow_head(skb, tot_len + dst_dev_overhead(cache_dst, skb));
if (unlikely(err))
return err;

Expand Down Expand Up @@ -197,11 +197,18 @@ int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, int proto)

return 0;
}

/* encapsulate an IPv6 packet within an outer IPv6 header with a given SRH */
int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, int proto)
{
return __seg6_do_srh_encap(skb, osrh, proto, NULL);
}
EXPORT_SYMBOL_GPL(seg6_do_srh_encap);

/* encapsulate an IPv6 packet within an outer IPv6 header with reduced SRH */
static int seg6_do_srh_encap_red(struct sk_buff *skb,
struct ipv6_sr_hdr *osrh, int proto)
struct ipv6_sr_hdr *osrh, int proto,
struct dst_entry *cache_dst)
{
__u8 first_seg = osrh->first_segment;
struct dst_entry *dst = skb_dst(skb);
Expand Down Expand Up @@ -230,7 +237,7 @@ static int seg6_do_srh_encap_red(struct sk_buff *skb,

tot_len = red_hdrlen + sizeof(struct ipv6hdr);

err = skb_cow_head(skb, tot_len + skb->mac_len);
err = skb_cow_head(skb, tot_len + dst_dev_overhead(cache_dst, skb));
if (unlikely(err))
return err;

Expand Down Expand Up @@ -317,16 +324,16 @@ static int seg6_do_srh_encap_red(struct sk_buff *skb,
return 0;
}

/* insert an SRH within an IPv6 packet, just after the IPv6 header */
int seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh)
static int __seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh,
struct dst_entry *cache_dst)
{
struct ipv6hdr *hdr, *oldhdr;
struct ipv6_sr_hdr *isrh;
int hdrlen, err;

hdrlen = (osrh->hdrlen + 1) << 3;

err = skb_cow_head(skb, hdrlen + skb->mac_len);
err = skb_cow_head(skb, hdrlen + dst_dev_overhead(cache_dst, skb));
if (unlikely(err))
return err;

Expand Down Expand Up @@ -369,9 +376,8 @@ int seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh)

return 0;
}
EXPORT_SYMBOL_GPL(seg6_do_srh_inline);

static int seg6_do_srh(struct sk_buff *skb)
static int seg6_do_srh(struct sk_buff *skb, struct dst_entry *cache_dst)
{
struct dst_entry *dst = skb_dst(skb);
struct seg6_iptunnel_encap *tinfo;
Expand All @@ -384,7 +390,7 @@ static int seg6_do_srh(struct sk_buff *skb)
if (skb->protocol != htons(ETH_P_IPV6))
return -EINVAL;

err = seg6_do_srh_inline(skb, tinfo->srh);
err = __seg6_do_srh_inline(skb, tinfo->srh, cache_dst);
if (err)
return err;
break;
Expand All @@ -402,9 +408,11 @@ static int seg6_do_srh(struct sk_buff *skb)
return -EINVAL;

if (tinfo->mode == SEG6_IPTUN_MODE_ENCAP)
err = seg6_do_srh_encap(skb, tinfo->srh, proto);
err = __seg6_do_srh_encap(skb, tinfo->srh,
proto, cache_dst);
else
err = seg6_do_srh_encap_red(skb, tinfo->srh, proto);
err = seg6_do_srh_encap_red(skb, tinfo->srh,
proto, cache_dst);

if (err)
return err;
Expand All @@ -425,11 +433,13 @@ static int seg6_do_srh(struct sk_buff *skb)
skb_push(skb, skb->mac_len);

if (tinfo->mode == SEG6_IPTUN_MODE_L2ENCAP)
err = seg6_do_srh_encap(skb, tinfo->srh,
IPPROTO_ETHERNET);
err = __seg6_do_srh_encap(skb, tinfo->srh,
IPPROTO_ETHERNET,
cache_dst);
else
err = seg6_do_srh_encap_red(skb, tinfo->srh,
IPPROTO_ETHERNET);
IPPROTO_ETHERNET,
cache_dst);

if (err)
return err;
Expand All @@ -444,6 +454,13 @@ static int seg6_do_srh(struct sk_buff *skb)
return 0;
}

/* insert an SRH within an IPv6 packet, just after the IPv6 header */
int seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh)
{
return __seg6_do_srh_inline(skb, osrh, NULL);
}
EXPORT_SYMBOL_GPL(seg6_do_srh_inline);

static int seg6_input_finish(struct net *net, struct sock *sk,
struct sk_buff *skb)
{
Expand All @@ -458,31 +475,33 @@ static int seg6_input_core(struct net *net, struct sock *sk,
struct seg6_lwt *slwt;
int err;

err = seg6_do_srh(skb);
if (unlikely(err))
goto drop;

slwt = seg6_lwt_lwtunnel(orig_dst->lwtstate);

local_bh_disable();
dst = dst_cache_get(&slwt->cache);
local_bh_enable();

err = seg6_do_srh(skb, dst);
if (unlikely(err))
goto drop;

if (!dst) {
ip6_route_input(skb);
dst = skb_dst(skb);
if (!dst->error) {
local_bh_disable();
dst_cache_set_ip6(&slwt->cache, dst,
&ipv6_hdr(skb)->saddr);
local_bh_enable();
}

err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
if (unlikely(err))
goto drop;
} else {
skb_dst_drop(skb);
skb_dst_set(skb, dst);
}
local_bh_enable();

err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
if (unlikely(err))
goto drop;

if (static_branch_unlikely(&nf_hooks_lwtunnel_enabled))
return NF_HOOK(NFPROTO_IPV6, NF_INET_LOCAL_OUT,
Expand Down Expand Up @@ -528,16 +547,16 @@ static int seg6_output_core(struct net *net, struct sock *sk,
struct seg6_lwt *slwt;
int err;

err = seg6_do_srh(skb);
if (unlikely(err))
goto drop;

slwt = seg6_lwt_lwtunnel(orig_dst->lwtstate);

local_bh_disable();
dst = dst_cache_get(&slwt->cache);
local_bh_enable();

err = seg6_do_srh(skb, dst);
if (unlikely(err))
goto drop;

if (unlikely(!dst)) {
struct ipv6hdr *hdr = ipv6_hdr(skb);
struct flowi6 fl6;
Expand All @@ -559,15 +578,15 @@ static int seg6_output_core(struct net *net, struct sock *sk,
local_bh_disable();
dst_cache_set_ip6(&slwt->cache, dst, &fl6.saddr);
local_bh_enable();

err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
if (unlikely(err))
goto drop;
}

skb_dst_drop(skb);
skb_dst_set(skb, dst);

err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
if (unlikely(err))
goto drop;

if (static_branch_unlikely(&nf_hooks_lwtunnel_enabled))
return NF_HOOK(NFPROTO_IPV6, NF_INET_LOCAL_OUT, net, sk, skb,
NULL, skb_dst(skb)->dev, dst_output);
Expand Down

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