Message ID | 1283145794-5615-4-git-send-email-gerrit@erg.abdn.ac.uk |
---|---|
State | Accepted, archived |
Delegated to: | David Miller |
Headers | show |
On Mon, 30 Aug 2010, Gerrit Renker wrote: > This patch consolidates initial-window code common to TCP and CCID-2: > * TCP uses RFC 3390 in a packet-oriented manner (tcp_input.c) and > * CCID-2 uses RFC 3390 in packet-oriented manner (RFC 4341). > > Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> > --- > include/net/tcp.h | 15 +++++++++++++++ > net/dccp/ccids/ccid2.c | 8 ++------ > net/ipv4/tcp_input.c | 17 ++--------------- > 3 files changed, 19 insertions(+), 21 deletions(-) > > --- a/include/net/tcp.h > +++ b/include/net/tcp.h > @@ -789,6 +789,21 @@ static inline __u32 tcp_current_ssthresh(const struct sock *sk) > /* Use define here intentionally to get WARN_ON location shown at the caller */ > #define tcp_verify_left_out(tp) WARN_ON(tcp_left_out(tp) > tp->packets_out) > > +/* > + * Convert RFC 3390 larger initial window into an equivalent number of packets. > + * > + * John Heffner states: > + * > + * The RFC specifies a window of no more than 4380 bytes > + * unless 2*MSS > 4380. Reading the pseudocode in the RFC > + * is a bit misleading because they use a clamp at 4380 bytes > + * rather than a multiplier in the relevant range. > + */ > +static inline u32 rfc3390_bytes_to_packets(const u32 smss) > +{ > + return smss <= 1095 ? 4 : (smss > 1460 ? 2 : 3); > +} > + > extern void tcp_enter_cwr(struct sock *sk, const int set_ssthresh); > extern __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst); > > --- a/net/dccp/ccids/ccid2.c > +++ b/net/dccp/ccids/ccid2.c > @@ -641,12 +641,8 @@ static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk) > /* RFC 4341, 5: initialise ssthresh to arbitrarily high (max) value */ > hc->tx_ssthresh = ~0U; > > - /* > - * RFC 4341, 5: "The cwnd parameter is initialized to at most four > - * packets for new connections, following the rules from [RFC3390]". > - * We need to convert the bytes of RFC3390 into the packets of RFC 4341. > - */ > - hc->tx_cwnd = clamp(4380U / dp->dccps_mss_cache, 2U, 4U); > + /* Use larger initial windows (RFC 4341, section 5). */ > + hc->tx_cwnd = rfc3390_bytes_to_packets(dp->dccps_mss_cache); > > /* Make sure that Ack Ratio is enabled and within bounds. */ > max_ratio = DIV_ROUND_UP(hc->tx_cwnd, 2); > --- a/net/ipv4/tcp_input.c > +++ b/net/ipv4/tcp_input.c > @@ -805,25 +805,12 @@ void tcp_update_metrics(struct sock *sk) > } > } > > -/* Numbers are taken from RFC3390. > - * > - * John Heffner states: > - * > - * The RFC specifies a window of no more than 4380 bytes > - * unless 2*MSS > 4380. Reading the pseudocode in the RFC > - * is a bit misleading because they use a clamp at 4380 bytes > - * rather than use a multiplier in the relevant range. > - */ > __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst) > { > __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0); > > - if (!cwnd) { > - if (tp->mss_cache > 1460) > - cwnd = 2; > - else > - cwnd = (tp->mss_cache > 1095) ? 3 : 4; > - } > + if (!cwnd) > + cwnd = rfc3390_bytes_to_packets(tp->mss_cache); > return min_t(__u32, cwnd, tp->snd_cwnd_clamp); > } What is spelled out in tcp_select_initial_window might also need to follow the same logic?
| > This patch consolidates initial-window code common to TCP and CCID-2: | > * TCP uses RFC 3390 in a packet-oriented manner (tcp_input.c) and | > * CCID-2 uses RFC 3390 in packet-oriented manner (RFC 4341). ... | > +static inline u32 rfc3390_bytes_to_packets(const u32 smss) | > +{ | > + return smss <= 1095 ? 4 : (smss > 1460 ? 2 : 3); | > +} | > + ... | | What is spelled out in tcp_select_initial_window might also need to follow | the same logic? | Thank you for paying attention, can you please have a look at the subsequent patch. I went through this yesterday and found that in 4 different places there are 4 different interpretations of what RFC 3390 means. Having asked someone more familiar with IETF issues, it seems that the RFC 5681 interpretation of RFC 3390 is now the 'official' one. +------------+--------------------+--------------------+--------------------+--------------------+ | Condition | RFC 2414 | Linux | Linux | RFC 5681 | | | RFC 3390 | tcp_input | tcp_output | | +------------+--------------------+--------------------+--------------------+--------------------+ | 2 segments | 2190 < MSS | 1460 < MSS | 4380 < MSS | 2190 < MSS | | 3 segments | 1095 < MSS <= 1460 | 1095 < MSS <= 1460 | 1460 < MSS <= 4380 | 1095 < MSS <= 2190 | | 4 segments | MSS <= 1095 | MSS <= 1095 | MSS <= 1460 | MSS <= 1095 | +------------+--------------------+--------------------+--------------------+--------------------+ -- 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
Hi Gerrit, Am 01.09.2010 um 07:23 schrieb Gerrit Renker: > | > This patch consolidates initial-window code common to TCP and CCID-2: > | > * TCP uses RFC 3390 in a packet-oriented manner (tcp_input.c) and > | > * CCID-2 uses RFC 3390 in packet-oriented manner (RFC 4341). > ... > | > +static inline u32 rfc3390_bytes_to_packets(const u32 smss) > | > +{ > | > + return smss <= 1095 ? 4 : (smss > 1460 ? 2 : 3); > | > +} > | > + > ... > | > | What is spelled out in tcp_select_initial_window might also need to follow > | the same logic? > | > Thank you for paying attention, can you please have a look at the subsequent > patch. I went through this yesterday and found that in 4 different places > there are 4 different interpretations of what RFC 3390 means. > > Having asked someone more familiar with IETF issues, it seems that the RFC 5681 > interpretation of RFC 3390 is now the 'official' one. > > +------------+--------------------+--------------------+--------------------+--------------------+ > | Condition | RFC 2414 | Linux | Linux | RFC 5681 | > | | RFC 3390 | tcp_input | tcp_output | | > +------------+--------------------+--------------------+--------------------+--------------------+ > | 2 segments | 2190 < MSS | 1460 < MSS | 4380 < MSS | 2190 < MSS | > | 3 segments | 1095 < MSS <= 1460 | 1095 < MSS <= 1460 | 1460 < MSS <= 4380 | 1095 < MSS <= 2190 | ^^^^^ Are you sure about this? RFC3390 says (page 2): If (1095 bytes < MSS < 2190 bytes) then win <= 4380; So, IMO it should be 1095 < MSS < 2190 for 3 segments, and 2190 <= MSS for 2 segments in the "RFC 3390" column. BTW: I think that we should not reference RFC2414, since RFC3390 obsoletes it. Alex > | 4 segments | MSS <= 1095 | MSS <= 1095 | MSS <= 1460 | MSS <= 1095 | > +------------+--------------------+--------------------+--------------------+--------------------+ > -- > 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 // // Dipl.-Inform. Alexander Zimmermann // Department of Computer Science, Informatik 4 // RWTH Aachen University // Ahornstr. 55, 52056 Aachen, Germany // phone: (49-241) 80-21422, fax: (49-241) 80-22221 // email: zimmermann@cs.rwth-aachen.de // web: http://www.umic-mesh.net //
--- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -789,6 +789,21 @@ static inline __u32 tcp_current_ssthresh(const struct sock *sk) /* Use define here intentionally to get WARN_ON location shown at the caller */ #define tcp_verify_left_out(tp) WARN_ON(tcp_left_out(tp) > tp->packets_out) +/* + * Convert RFC 3390 larger initial window into an equivalent number of packets. + * + * John Heffner states: + * + * The RFC specifies a window of no more than 4380 bytes + * unless 2*MSS > 4380. Reading the pseudocode in the RFC + * is a bit misleading because they use a clamp at 4380 bytes + * rather than a multiplier in the relevant range. + */ +static inline u32 rfc3390_bytes_to_packets(const u32 smss) +{ + return smss <= 1095 ? 4 : (smss > 1460 ? 2 : 3); +} + extern void tcp_enter_cwr(struct sock *sk, const int set_ssthresh); extern __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst); --- a/net/dccp/ccids/ccid2.c +++ b/net/dccp/ccids/ccid2.c @@ -641,12 +641,8 @@ static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk) /* RFC 4341, 5: initialise ssthresh to arbitrarily high (max) value */ hc->tx_ssthresh = ~0U; - /* - * RFC 4341, 5: "The cwnd parameter is initialized to at most four - * packets for new connections, following the rules from [RFC3390]". - * We need to convert the bytes of RFC3390 into the packets of RFC 4341. - */ - hc->tx_cwnd = clamp(4380U / dp->dccps_mss_cache, 2U, 4U); + /* Use larger initial windows (RFC 4341, section 5). */ + hc->tx_cwnd = rfc3390_bytes_to_packets(dp->dccps_mss_cache); /* Make sure that Ack Ratio is enabled and within bounds. */ max_ratio = DIV_ROUND_UP(hc->tx_cwnd, 2); --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -805,25 +805,12 @@ void tcp_update_metrics(struct sock *sk) } } -/* Numbers are taken from RFC3390. - * - * John Heffner states: - * - * The RFC specifies a window of no more than 4380 bytes - * unless 2*MSS > 4380. Reading the pseudocode in the RFC - * is a bit misleading because they use a clamp at 4380 bytes - * rather than use a multiplier in the relevant range. - */ __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst) { __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0); - if (!cwnd) { - if (tp->mss_cache > 1460) - cwnd = 2; - else - cwnd = (tp->mss_cache > 1095) ? 3 : 4; - } + if (!cwnd) + cwnd = rfc3390_bytes_to_packets(tp->mss_cache); return min_t(__u32, cwnd, tp->snd_cwnd_clamp); }
This patch consolidates initial-window code common to TCP and CCID-2: * TCP uses RFC 3390 in a packet-oriented manner (tcp_input.c) and * CCID-2 uses RFC 3390 in packet-oriented manner (RFC 4341). Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> --- include/net/tcp.h | 15 +++++++++++++++ net/dccp/ccids/ccid2.c | 8 ++------ net/ipv4/tcp_input.c | 17 ++--------------- 3 files changed, 19 insertions(+), 21 deletions(-) -- 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