| Message ID | 20241025133727.27742-2-justin.iurman@uliege.be (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | Mitigate the two-reallocations issue for iptunnels | expand |
From: Justin Iurman <justin.iurman@uliege.be> Date: Fri, 25 Oct 2024 15:37:25 +0200 > This patch mitigates the two-reallocations issue with ioam6_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. [...] > static int ioam6_do_inline(struct net *net, struct sk_buff *skb, > - struct ioam6_lwt_encap *tuninfo) > + struct ioam6_lwt_encap *tuninfo, > + struct dst_entry *dst) > { > struct ipv6hdr *oldhdr, *hdr; > int hdrlen, err; > > hdrlen = (tuninfo->eh.hdrlen + 1) << 3; > > - err = skb_cow_head(skb, hdrlen + skb->mac_len); > + err = skb_cow_head(skb, hdrlen + (!dst ? skb->mac_len > + : LL_RESERVED_SPACE(dst->dev))); You use this pattern a lot throughout the series. I believe you should make a static inline or a macro from it. static inline u32 some_name(const *dst, const *skb) { return dst ? LL_RESERVED_SPACE(dst->dev) : skb->mac_len; } BTW why do you check for `!dst`, not `dst`? Does changing this affects performance? > if (unlikely(err)) > return err; Thanks, Olek
On 10/25/24 17:12, Alexander Lobakin wrote: > From: Justin Iurman <justin.iurman@uliege.be> > Date: Fri, 25 Oct 2024 15:37:25 +0200 > >> This patch mitigates the two-reallocations issue with ioam6_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. > > [...] > >> static int ioam6_do_inline(struct net *net, struct sk_buff *skb, >> - struct ioam6_lwt_encap *tuninfo) >> + struct ioam6_lwt_encap *tuninfo, >> + struct dst_entry *dst) >> { >> struct ipv6hdr *oldhdr, *hdr; >> int hdrlen, err; >> >> hdrlen = (tuninfo->eh.hdrlen + 1) << 3; >> >> - err = skb_cow_head(skb, hdrlen + skb->mac_len); >> + err = skb_cow_head(skb, hdrlen + (!dst ? skb->mac_len >> + : LL_RESERVED_SPACE(dst->dev))); > > You use this pattern a lot throughout the series. I believe you should > make a static inline or a macro from it. > > static inline u32 some_name(const *dst, const *skb) > { > return dst ? LL_RESERVED_SPACE(dst->dev) : skb->mac_len; > } > > BTW why do you check for `!dst`, not `dst`? Does changing this affects > performance? Not at all, you're right... even the opposite actually. Regarding the static inline suggestion, it could be a good idea and may even look like this as an optimization: static inline u32 dev_overhead(struct dst_entry *dst, struct sk_buff *skb) { if (likely(dst)) return LL_RESERVED_SPACE(dst->dev); return skb->mac_len; } The question is... where should it go then? A static inline function per file (i.e., ioam6_iptunnel.c, seg6_iptunnel.c, and rpl_iptunnel.c)? In that case, it would still be repeated 3 times. Or in a header file somewhere, to have it defined only once? If so, what location do you think would be best?
From: Justin Iurman <justin.iurman@uliege.be> Date: Fri, 25 Oct 2024 23:06:36 +0200 > On 10/25/24 17:12, Alexander Lobakin wrote: >> From: Justin Iurman <justin.iurman@uliege.be> >> Date: Fri, 25 Oct 2024 15:37:25 +0200 >> >>> This patch mitigates the two-reallocations issue with ioam6_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. >> >> [...] >> >>> static int ioam6_do_inline(struct net *net, struct sk_buff *skb, >>> - struct ioam6_lwt_encap *tuninfo) >>> + struct ioam6_lwt_encap *tuninfo, >>> + struct dst_entry *dst) >>> { >>> struct ipv6hdr *oldhdr, *hdr; >>> int hdrlen, err; >>> hdrlen = (tuninfo->eh.hdrlen + 1) << 3; >>> - err = skb_cow_head(skb, hdrlen + skb->mac_len); >>> + err = skb_cow_head(skb, hdrlen + (!dst ? skb->mac_len >>> + : LL_RESERVED_SPACE(dst->dev))); >> >> You use this pattern a lot throughout the series. I believe you should >> make a static inline or a macro from it. >> >> static inline u32 some_name(const *dst, const *skb) >> { >> return dst ? LL_RESERVED_SPACE(dst->dev) : skb->mac_len; >> } >> >> BTW why do you check for `!dst`, not `dst`? Does changing this affects >> performance? > > Not at all, you're right... even the opposite actually. Regarding the > static inline suggestion, it could be a good idea and may even look like > this as an optimization: > > static inline u32 dev_overhead(struct dst_entry *dst, struct sk_buff *skb) > { > if (likely(dst)) > return LL_RESERVED_SPACE(dst->dev); > > return skb->mac_len; > } Oh, nice! > > The question is... where should it go then? A static inline function per > file (i.e., ioam6_iptunnel.c, seg6_iptunnel.c, and rpl_iptunnel.c)? In > that case, it would still be repeated 3 times. Or in a header file > somewhere, to have it defined only once? If so, what location do you > think would be best? 100% should be in a header file. Can't suggest any since I don't usually work with tunnels and ain't deep into its header structure. Thanks, Olek
diff --git a/net/ipv6/ioam6_iptunnel.c b/net/ipv6/ioam6_iptunnel.c index beb6b4cfc551..da79055fc02a 100644 --- a/net/ipv6/ioam6_iptunnel.c +++ b/net/ipv6/ioam6_iptunnel.c @@ -255,14 +255,16 @@ static int ioam6_do_fill(struct net *net, struct sk_buff *skb) } static int ioam6_do_inline(struct net *net, struct sk_buff *skb, - struct ioam6_lwt_encap *tuninfo) + struct ioam6_lwt_encap *tuninfo, + struct dst_entry *dst) { struct ipv6hdr *oldhdr, *hdr; int hdrlen, err; hdrlen = (tuninfo->eh.hdrlen + 1) << 3; - err = skb_cow_head(skb, hdrlen + skb->mac_len); + err = skb_cow_head(skb, hdrlen + (!dst ? skb->mac_len + : LL_RESERVED_SPACE(dst->dev))); if (unlikely(err)) return err; @@ -293,16 +295,17 @@ static int ioam6_do_encap(struct net *net, struct sk_buff *skb, struct ioam6_lwt_encap *tuninfo, bool has_tunsrc, struct in6_addr *tunsrc, - struct in6_addr *tundst) + struct in6_addr *tundst, + struct dst_entry *dst) { - struct dst_entry *dst = skb_dst(skb); struct ipv6hdr *hdr, *inner_hdr; int hdrlen, len, err; hdrlen = (tuninfo->eh.hdrlen + 1) << 3; len = sizeof(*hdr) + hdrlen; - err = skb_cow_head(skb, len + skb->mac_len); + err = skb_cow_head(skb, len + (!dst ? skb->mac_len + : LL_RESERVED_SPACE(dst->dev))); if (unlikely(err)) return err; @@ -326,7 +329,7 @@ static int ioam6_do_encap(struct net *net, struct sk_buff *skb, if (has_tunsrc) memcpy(&hdr->saddr, tunsrc, sizeof(*tunsrc)); else - ipv6_dev_get_saddr(net, dst->dev, &hdr->daddr, + ipv6_dev_get_saddr(net, skb_dst(skb)->dev, &hdr->daddr, IPV6_PREFER_SRC_PUBLIC, &hdr->saddr); skb_postpush_rcsum(skb, hdr, len); @@ -336,7 +339,7 @@ static int ioam6_do_encap(struct net *net, struct sk_buff *skb, static int ioam6_output(struct net *net, struct sock *sk, struct sk_buff *skb) { - struct dst_entry *dst = skb_dst(skb); + struct dst_entry *dst, *orig_dst = skb_dst(skb); struct in6_addr orig_daddr; struct ioam6_lwt *ilwt; int err = -EINVAL; @@ -345,7 +348,7 @@ static int ioam6_output(struct net *net, struct sock *sk, struct sk_buff *skb) if (skb->protocol != htons(ETH_P_IPV6)) goto drop; - ilwt = ioam6_lwt_state(dst->lwtstate); + ilwt = ioam6_lwt_state(orig_dst->lwtstate); /* Check for insertion frequency (i.e., "k over n" insertions) */ pkt_cnt = atomic_fetch_inc(&ilwt->pkt_cnt); @@ -354,6 +357,10 @@ static int ioam6_output(struct net *net, struct sock *sk, struct sk_buff *skb) orig_daddr = ipv6_hdr(skb)->daddr; + local_bh_disable(); + dst = dst_cache_get(&ilwt->cache); + local_bh_enable(); + switch (ilwt->mode) { case IOAM6_IPTUNNEL_MODE_INLINE: do_inline: @@ -361,7 +368,7 @@ static int ioam6_output(struct net *net, struct sock *sk, struct sk_buff *skb) if (ipv6_hdr(skb)->nexthdr == NEXTHDR_HOP) goto out; - err = ioam6_do_inline(net, skb, &ilwt->tuninfo); + err = ioam6_do_inline(net, skb, &ilwt->tuninfo, dst); if (unlikely(err)) goto drop; @@ -371,7 +378,7 @@ static int ioam6_output(struct net *net, struct sock *sk, struct sk_buff *skb) /* Encapsulation (ip6ip6) */ err = ioam6_do_encap(net, skb, &ilwt->tuninfo, ilwt->has_tunsrc, &ilwt->tunsrc, - &ilwt->tundst); + &ilwt->tundst, dst); if (unlikely(err)) goto drop; @@ -389,45 +396,40 @@ static int ioam6_output(struct net *net, struct sock *sk, struct sk_buff *skb) goto drop; } - err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev)); - if (unlikely(err)) - goto drop; + if (unlikely(!dst)) { + struct ipv6hdr *hdr = ipv6_hdr(skb); + struct flowi6 fl6; + + memset(&fl6, 0, sizeof(fl6)); + fl6.daddr = hdr->daddr; + fl6.saddr = hdr->saddr; + fl6.flowlabel = ip6_flowinfo(hdr); + fl6.flowi6_mark = skb->mark; + fl6.flowi6_proto = hdr->nexthdr; + + dst = ip6_route_output(net, NULL, &fl6); + if (dst->error) { + err = dst->error; + dst_release(dst); + goto drop; + } - if (!ipv6_addr_equal(&orig_daddr, &ipv6_hdr(skb)->daddr)) { local_bh_disable(); - dst = dst_cache_get(&ilwt->cache); + dst_cache_set_ip6(&ilwt->cache, dst, &fl6.saddr); local_bh_enable(); - if (unlikely(!dst)) { - struct ipv6hdr *hdr = ipv6_hdr(skb); - struct flowi6 fl6; - - memset(&fl6, 0, sizeof(fl6)); - fl6.daddr = hdr->daddr; - fl6.saddr = hdr->saddr; - fl6.flowlabel = ip6_flowinfo(hdr); - fl6.flowi6_mark = skb->mark; - fl6.flowi6_proto = hdr->nexthdr; - - dst = ip6_route_output(net, NULL, &fl6); - if (dst->error) { - err = dst->error; - dst_release(dst); - goto drop; - } - - local_bh_disable(); - dst_cache_set_ip6(&ilwt->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); + skb_dst_drop(skb); + skb_dst_set(skb, dst); + if (!ipv6_addr_equal(&orig_daddr, &ipv6_hdr(skb)->daddr)) return dst_output(net, sk, skb); - } out: - return dst->lwtstate->orig_output(net, sk, skb); + return orig_dst->lwtstate->orig_output(net, sk, skb); drop: kfree_skb(skb); return err;
This patch mitigates the two-reallocations issue with ioam6_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: - inline mode: - before: https://ibb.co/LhQ8V63 - after: https://ibb.co/x5YT2bS - encap mode: - before: https://ibb.co/3Cjm5m0 - after: https://ibb.co/TwpsxTC - encap mode with tunsrc: - before: https://ibb.co/Gpy9QPg - after: https://ibb.co/PW1bZFT This patch also fixes an incorrect behavior: after the insertion, the second call to skb_cow_head() makes sure that the dev has enough headroom in the skb for layer 2 and stuff. In that case, the "old" dst_entry was used, which is now fixed. After discussing with Paolo, it appears that both patches can be merged into a single one -this one- (for the sake of readability) and target net-next. Signed-off-by: Justin Iurman <justin.iurman@uliege.be> --- net/ipv6/ioam6_iptunnel.c | 84 ++++++++++++++++++++------------------- 1 file changed, 43 insertions(+), 41 deletions(-)