On Mon, 25 Jun 2007 22:09:39 +0900 (JST)
OBATA Noboru <[EMAIL PROTECTED]> wrote:
> From: OBATA Noboru <[EMAIL PROTECTED]>
>
> Make TCP_RTO_MAX a variable, and allow a user to change it via a
> new sysctl entry /proc/sys/net/ipv4/tcp_rto_max. A user can
> then guarantee TCP retransmission to be more controllable, say,
> at least once per 10 seconds, by setting it to 10. This is
> quite helpful on failover-capable network devices, such as an
> active-backup bonding device. On such devices, it is desirable
> that TCP retransmits a packet shortly after the failover, which
> is what I would like to do with this patch. Please see
> Background and Problem below for rationale in detail.
>
> Reading from /proc/sys/net/ipv4/tcp_rto_max shows the current
> TCP_RTO_MAX in seconds. The actual value of TCP_RTO_MAX is
> stored in sysctl_tcp_rto_max in jiffies.
>
> Writing to /proc/sys/net/ipv4/tcp_rto_max updates the
> TCP_RTO_MAX, only if the new value is not smaller than
> TCP_RTO_MIN, which is currently 0.2[sec]. Since tcp_rto_max is
> an integer, the minimum value of /proc/sys/net/ipv4/tcp_rto_max
> is 1, in substance. Also the RtoMax entry in /proc/net/snmp is
> updated.
>
> Please note that this is effective in IPv6 as well.
>
>
> Background and Problem
> ======================
>
> When designing a TCP/IP based network system on failover-capable
> network devices, people want to set timeouts hierarchically in
> three layers, network device layer, TCP layer, and application
> layer (bottom-up order), such that:
>
> 1. Network device layer detects a failure first and switch to a
> backup device (say, in 20sec).
>
> 2. TCP layer timeout & retransmission comes next, _hopefully_
> before the application layer timeout.
>
> 3. Application layer detects a network failure last (by, say,
> 30sec timeout) and may trigger a system-level failover.
>
> * Note 1. The timeouts for #1 and #2 are handled
> independently and there is no relationship between them.
>
> * Note 2. The actual timeout settings (20sec or 30sec in
> this example) are often determined by systems requirement
> and so setting them to certain "safe values" (if any) are
> usually not possible.
>
> If TCP retransmission misses the time frame between event #1
> and #3 in Background above (between 20 and 30sec since network
> failure), a failure causes the system-level failover where the
> network-device-level failover should be enough.
>
> The problem in this hierarchical timeout scheme is that TCP
> layer does not guarantee the next retransmission to occur in
> certain period of time. In the above example, people expect TCP
> to retransmit a packet between 20 and 30sec since network
> failure, but it may not happen.
>
> Starting from RTO=0.5sec for example, retransmission will occur
> at time 0.5, 1.5, 3.5, 7.5, 15.5, and 31.5 as indicated by 'o'
> in the following diagram, but miss the time frame between time
> 20 and 30.
>
> time: 0 10 20 30sec
> | | | |
> App. layer |---------+---------+---------X ==> system failover
> TCP layer oo-o---o--+----o----+---------+o <== expects retrans. b/w 20~30
> Netdev layer |---------+---------X ==> network failover
>
>
> Signed-off-by: OBATA Noboru <[EMAIL PROTECTED]>
> ---
>
> Documentation/networking/ip-sysctl.txt | 6 +
> include/linux/sysctl.h | 1
> include/net/tcp.h | 5 +
> net/ipv4/sysctl_net_ipv4.c | 77 +++++++++++++++++++++++++
> net/ipv4/tcp_timer.c | 3
> 5 files changed, 91 insertions(+), 1 deletion(-)
>
> diff -uprN -X a/Documentation/dontdiff
> linux-2.6.22-rc5-orig/Documentation/networking/ip-sysctl.txt
> b/Documentation/networking/ip-sysctl.txt
> --- a/Documentation/networking/ip-sysctl.txt 2007-06-22 21:34:18.000000000
> +0900
> +++ b/Documentation/networking/ip-sysctl.txt 2007-06-25 16:07:21.000000000
> +0900
> @@ -340,6 +340,12 @@ tcp_rmem - vector of 3 INTEGERs: min, de
> net.core.rmem_max, "static" selection via SO_RCVBUF does not use this.
> Default: 87380*2 bytes.
>
> +tcp_rto_max - INTEGER
> + Maximum time in seconds to which RTO can grow. Exponential
> + backoff of RTO is bounded by this value. The value must not be
> + smaller than 1. Note this parameter is also effective for IPv6.
> + Default: 120
> +
> tcp_sack - BOOLEAN
> Enable select acknowledgments (SACKS).
>
> diff -uprN -X a/Documentation/dontdiff
> linux-2.6.22-rc5-orig/include/linux/sysctl.h b/include/linux/sysctl.h
> --- a/include/linux/sysctl.h 2007-06-22 21:34:33.000000000 +0900
> +++ b/include/linux/sysctl.h 2007-06-25 16:27:29.000000000 +0900
> @@ -441,6 +441,7 @@ enum
> NET_TCP_ALLOWED_CONG_CONTROL=123,
> NET_TCP_MAX_SSTHRESH=124,
> NET_TCP_FRTO_RESPONSE=125,
> + NET_TCP_RTO_MAX=126,
> };
>
Rather than assigning another numeric sysctl value, you can use
CTL_UNNUMBERED. The use of numeric sysctl's is being phased down, at one
point they were even going to be deprecated.
> enum {
> diff -uprN -X a/Documentation/dontdiff
> linux-2.6.22-rc5-orig/include/net/tcp.h b/include/net/tcp.h
> --- a/include/net/tcp.h 2007-06-22 21:34:33.000000000 +0900
> +++ b/include/net/tcp.h 2007-06-22 21:40:05.000000000 +0900
> @@ -121,7 +121,9 @@ extern void tcp_time_wait(struct sock *s
> #define TCP_DELACK_MIN 4U
> #define TCP_ATO_MIN 4U
> #endif
> -#define TCP_RTO_MAX ((unsigned)(120*HZ))
> +extern int sysctl_tcp_rto_max;
> +#define TCP_RTO_MAX ((unsigned)(sysctl_tcp_rto_max))
> +#define TCP_RTO_MAX_DEFAULT ((unsigned)(120*HZ))
> #define TCP_RTO_MIN ((unsigned)(HZ/5))
> #define TCP_TIMEOUT_INIT ((unsigned)(3*HZ)) /* RFC 1122 initial RTO value
> */
Rather than causing macro TCP_RTO_MAX to reference sysctl_rto_max directly.
> @@ -203,6 +205,7 @@ extern int sysctl_tcp_synack_retries;
> extern int sysctl_tcp_retries1;
> extern int sysctl_tcp_retries2;
> extern int sysctl_tcp_orphan_retries;
> +extern int sysctl_tcp_rto_max;
> extern int sysctl_tcp_syncookies;
> extern int sysctl_tcp_retrans_collapse;
> extern int sysctl_tcp_stdurg;
> diff -uprN -X a/Documentation/dontdiff
> linux-2.6.22-rc5-orig/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
> --- a/net/ipv4/sysctl_net_ipv4.c 2007-06-22 21:34:33.000000000 +0900
> +++ b/net/ipv4/sysctl_net_ipv4.c 2007-06-25 16:27:53.000000000 +0900
> @@ -186,6 +186,74 @@ static int strategy_allowed_congestion_c
>
> }
>
> +static int proc_tcp_rto_max(ctl_table *ctl, int write, struct file *filp,
> + void __user *buffer, size_t *lenp, loff_t *ppos)
> +{
> + int val = *(int *)ctl->data;
> + int ret;
> +
> + ret = proc_dointvec_jiffies(ctl, write, filp, buffer, lenp, ppos);
> + if (ret)
> + return ret;
> +
> + if (write && *(int *)ctl->data != val) {
> + if (*(int *)ctl->data < TCP_RTO_MIN) {
> + *(int *)ctl->data = val;
> + return -EINVAL;
> + }
> + TCP_ADD_STATS_USER(TCP_MIB_RTOMAX,
> + (*(int *)ctl->data - val) * 1000 / HZ);
> + }
> +
> + return 0;
> +}
> +
> +static int strategy_tcp_rto_max(ctl_table *table, int __user *name,
> + int nlen, void __user *oldval,
> + size_t __user *oldlenp,
> + void __user *newval, size_t newlen)
> +{
> + int *valp = table->data;
> + int new;
> +
> + if (!newval || !newlen)
> + return 0;
> +
> + if (newlen != sizeof(int))
> + return -EINVAL;
> +
> + if (get_user(new, (int __user *)newval))
> + return -EFAULT;
> +
> + if (new * HZ == *valp)
> + return 0;
> +
> + if (new * HZ < TCP_RTO_MIN)
> + return -EINVAL;
> +
> + if (oldval && oldlenp) {
> + size_t len;
> +
> + if (get_user(len, oldlenp))
> + return -EFAULT;
> +
> + if (len) {
> + if (len > table->maxlen)
> + len = table->maxlen;
> + if (put_user(*valp / HZ, (int __user *)oldval))
> + return -EFAULT;
> + if (put_user(len, oldlenp))
> + return -EFAULT;
> + }
> + }
> +
> + TCP_ADD_STATS_USER(TCP_MIB_RTOMAX, (new * HZ - *valp) * 1000 / HZ);
> +
> + *valp = new * HZ;
> +
> + return 1;
> +}
Could sysctl_rto_max be unsigned instead of int to avoid possible sign wrap
issues and
having to cast it on each use?
> ctl_table ipv4_table[] = {
> {
> .ctl_name = NET_IPV4_TCP_TIMESTAMPS,
> @@ -363,6 +431,15 @@ ctl_table ipv4_table[] = {
> .proc_handler = &proc_dointvec
> },
> {
> + .ctl_name = NET_TCP_RTO_MAX,
> + .procname = "tcp_rto_max",
> + .data = &sysctl_tcp_rto_max,
> + .maxlen = sizeof(int),
> + .mode = 0644,
> + .proc_handler = &proc_tcp_rto_max,
> + .strategy = &strategy_tcp_rto_max
> + },
> + {
> .ctl_name = NET_IPV4_TCP_FIN_TIMEOUT,
> .procname = "tcp_fin_timeout",
> .data = &sysctl_tcp_fin_timeout,
> diff -uprN -X a/Documentation/dontdiff
> linux-2.6.22-rc5-orig/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
> --- a/net/ipv4/tcp_timer.c 2007-06-22 21:34:33.000000000 +0900
> +++ b/net/ipv4/tcp_timer.c 2007-06-22 21:39:35.000000000 +0900
> @@ -31,6 +31,9 @@ int sysctl_tcp_keepalive_intvl __read_mo
> int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;
> int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
> int sysctl_tcp_orphan_retries __read_mostly;
> +int sysctl_tcp_rto_max __read_mostly = TCP_RTO_MAX_DEFAULT;
> +
> +EXPORT_SYMBOL(sysctl_tcp_rto_max);
>
> static void tcp_write_timer(unsigned long);
> static void tcp_delack_timer(unsigned long);
--
Stephen Hemminger <[EMAIL PROTECTED]>
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