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Date: Tue, 27 May 2008 07:42:02 +0200
From: Eric Dumazet <dada1@...mosbay.com>
To: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Cc: David Miller <davem@...emloft.net>, Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 2/2] [TCP]: Reorganize tcp_sock to fill 64-bit holes &
improve locality
Ilpo Järvinen a écrit :
> I tried to group recovery related fields nearby (non-CA_Open
> related variables, to be more accurate) so that one to three
> cachelines would not be necessary in CA_Open. These are now
> contiguously deployed:
>
> struct sk_buff_head out_of_order_queue; /* 1968 80 */
> /* --- cacheline 32 boundary (2048 bytes) --- */
> struct tcp_sack_block duplicate_sack[1]; /* 2048 8 */
> struct tcp_sack_block selective_acks[4]; /* 2056 32 */
> struct tcp_sack_block recv_sack_cache[4]; /* 2088 32 */
> /* --- cacheline 33 boundary (2112 bytes) was 8 bytes ago --- */
> struct sk_buff * highest_sack; /* 2120 8 */
> int lost_cnt_hint; /* 2128 4 */
> int retransmit_cnt_hint; /* 2132 4 */
> u32 lost_retrans_low; /* 2136 4 */
> u8 reordering; /* 2140 1 */
> u8 keepalive_probes; /* 2141 1 */
>
> /* XXX 2 bytes hole, try to pack */
>
> u32 prior_ssthresh; /* 2144 4 */
> u32 high_seq; /* 2148 4 */
> u32 retrans_stamp; /* 2152 4 */
> u32 undo_marker; /* 2156 4 */
> int undo_retrans; /* 2160 4 */
> u32 total_retrans; /* 2164 4 */
>
> ...and they're then followed by URG slowpath & keepalive related
> variables.
>
> Head of the out_of_order_queue always needed for empty checks,
> if that's empty (and TCP is in CA_Open), following ~200 bytes
> (in 64-bit) shouldn't be necessary for anything. If only OFO
> queue exists but TCP is in CA_Open, selective_acks (and possibly
> duplicate_sack) are necessary besides the out_of_order_queue
> but the rest of the block again shouldn't be (ie., the other
> direction had losses).
>
> As the cacheline boundaries depend on many factors in the
> preceeding stuff, trying to align considering them doesn't
> make too much sense.
>
> Commented one ordering hazard.
>
> There are number of low utilized u8/16s that could be combined
> get 2 bytes less in total so that the hole could be made to vanish
> (includes at least ecn_flags, urg_data, urg_mode, frto_counter,
> nonagle).
>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
> Cc: Eric Dumazet <dada1@...mosbay.com>
>
Thanks Ilpo for this work. This looks very good.
Sorry for my delayed answer.
Acked-by: Eric Dumazet <dada1@...mosbay.com>
> ---
>
> I'm not sure if this is a right time for such reorganization but it won't
> hurt to post it anyway.
>
> include/linux/tcp.h | 50 +++++++++++++++++++++++++-------------------------
> 1 files changed, 25 insertions(+), 25 deletions(-)
>
> diff --git a/include/linux/tcp.h b/include/linux/tcp.h
> index 18e62e3..9881295 100644
> --- a/include/linux/tcp.h
> +++ b/include/linux/tcp.h
> @@ -296,10 +296,9 @@ struct tcp_sock {
> u32 rcv_ssthresh; /* Current window clamp */
>
> u32 frto_highmark; /* snd_nxt when RTO occurred */
> - u8 reordering; /* Packet reordering metric. */
> + u16 advmss; /* Advertised MSS */
> u8 frto_counter; /* Number of new acks after RTO */
> u8 nonagle; /* Disable Nagle algorithm? */
> - u8 keepalive_probes; /* num of allowed keep alive probes */
>
> /* RTT measurement */
> u32 srtt; /* smoothed round trip time << 3 */
> @@ -310,6 +309,10 @@ struct tcp_sock {
>
> u32 packets_out; /* Packets which are "in flight" */
> u32 retrans_out; /* Retransmitted packets out */
> +
> + u16 urg_data; /* Saved octet of OOB data and control flags */
> + u8 urg_mode; /* In urgent mode */
> + u8 ecn_flags; /* ECN status bits. */
> /*
> * Options received (usually on last packet, some only on SYN packets).
> */
> @@ -325,13 +328,24 @@ struct tcp_sock {
> u32 snd_cwnd_used;
> u32 snd_cwnd_stamp;
>
> - struct sk_buff_head out_of_order_queue; /* Out of order segments go here */
> -
> u32 rcv_wnd; /* Current receiver window */
> u32 write_seq; /* Tail(+1) of data held in tcp send buffer */
> u32 pushed_seq; /* Last pushed seq, required to talk to windows */
> + u32 lost_out; /* Lost packets */
> + u32 sacked_out; /* SACK'd packets */
> + u32 fackets_out; /* FACK'd packets */
> + u32 tso_deferred;
> + u32 bytes_acked; /* Appropriate Byte Counting - RFC3465 */
>
> -/* SACKs data */
> + /* from STCP, retrans queue hinting */
> + struct sk_buff* lost_skb_hint;
> + struct sk_buff *scoreboard_skb_hint;
> + struct sk_buff *retransmit_skb_hint;
> + struct sk_buff *forward_skb_hint;
> +
> + struct sk_buff_head out_of_order_queue; /* Out of order segments go here */
> +
> + /* SACKs data, these 2 need to be together (see tcp_build_and_update_options) */
> struct tcp_sack_block duplicate_sack[1]; /* D-SACK block */
> struct tcp_sack_block selective_acks[4]; /* The SACKS themselves*/
>
> @@ -342,23 +356,14 @@ struct tcp_sock {
> * sacked_out > 0)
> */
>
> - /* from STCP, retrans queue hinting */
> - struct sk_buff* lost_skb_hint;
> -
> - struct sk_buff *scoreboard_skb_hint;
> - struct sk_buff *retransmit_skb_hint;
> - struct sk_buff *forward_skb_hint;
> -
> int lost_cnt_hint;
> int retransmit_cnt_hint;
>
> u32 lost_retrans_low; /* Sent seq after any rxmit (lowest) */
>
> - u16 advmss; /* Advertised MSS */
> + u8 reordering; /* Packet reordering metric. */
> + u8 keepalive_probes; /* num of allowed keep alive probes */
> u32 prior_ssthresh; /* ssthresh saved at recovery start */
> - u32 lost_out; /* Lost packets */
> - u32 sacked_out; /* SACK'd packets */
> - u32 fackets_out; /* FACK'd packets */
> u32 high_seq; /* snd_nxt at onset of congestion */
>
> u32 retrans_stamp; /* Timestamp of the last retransmit,
> @@ -366,25 +371,18 @@ struct tcp_sock {
> * the first SYN. */
> u32 undo_marker; /* tracking retrans started here. */
> int undo_retrans; /* number of undoable retransmissions. */
> + u32 total_retrans; /* Total retransmits for entire connection */
> +
> u32 urg_seq; /* Seq of received urgent pointer */
> - u16 urg_data; /* Saved octet of OOB data and control flags */
> - u8 urg_mode; /* In urgent mode */
> - u8 ecn_flags; /* ECN status bits. */
> u32 snd_up; /* Urgent pointer */
>
> - u32 total_retrans; /* Total retransmits for entire connection */
> - u32 bytes_acked; /* Appropriate Byte Counting - RFC3465 */
> -
> unsigned int keepalive_time; /* time before keep alive takes place */
> unsigned int keepalive_intvl; /* time interval between keep alive probes */
> - int linger2;
>
> struct tcp_deferred_accept_info defer_tcp_accept;
>
> unsigned long last_synq_overflow;
>
> - u32 tso_deferred;
> -
> /* Receiver side RTT estimation */
> struct {
> u32 rtt;
> @@ -412,6 +410,8 @@ struct tcp_sock {
> /* TCP MD5 Signagure Option information */
> struct tcp_md5sig_info *md5sig_info;
> #endif
> +
> + int linger2;
> };
>
> static inline struct tcp_sock *tcp_sk(const struct sock *sk)
>
--
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