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issue: 4043157 Set initial RTO to 1 second per RFC 6298 #498

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issue: 4043157 Set initial RTO to 1 second per RFC 6298 #498

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1 change: 1 addition & 0 deletions README
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Original file line number Diff line number Diff line change
Expand Up @@ -693,6 +693,7 @@ Maps to **XLIO_TCP_TIMER_RESOLUTION_MSEC** environment variable.
Control internal TCP timer resolution (fast timer) in milliseconds.
Minimum value is the thread wakeup timer resolution configured in
performance.threading.internal_handler.timer_msec.
Maximum is 500ms per RFC 1122 Section 4.2.3.2 (delayed ACK timer must not exceed 500ms).
Default value is 100

network.protocols.tcp.timestamps
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3 changes: 2 additions & 1 deletion src/core/config/descriptor_providers/xlio_config_schema.json
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Expand Up @@ -418,9 +418,10 @@
"timer_msec": {
"type": "integer",
"minimum": 0,
"maximum": 500,
"default": 100,
"title": "TCP timer interval (msec)",
"description": "Maps to XLIO_TCP_TIMER_RESOLUTION_MSEC environment variable.\nControl internal TCP timer resolution (fast timer) in milliseconds.\nMinimum value is the thread wakeup timer resolution configured in\nperformance.threading.internal_handler.timer_msec."
"description": "Maps to XLIO_TCP_TIMER_RESOLUTION_MSEC environment variable.\nControl internal TCP timer resolution (fast timer) in milliseconds.\nMinimum value is the thread wakeup timer resolution configured in\nperformance.threading.internal_handler.timer_msec.\nMaximum is 500ms per RFC 1122 Section 4.2.3.2 (delayed ACK timer must not exceed 500ms)."
},
"mss": {
"type": "integer",
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15 changes: 11 additions & 4 deletions src/core/lwip/tcp.c
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Expand Up @@ -905,6 +905,11 @@ err_t tcp_recv_null(void *arg, struct tcp_pcb *pcb, struct pbuf *p, err_t err)
return ERR_OK;
}

static inline u32_t get_initial_rto(void)
{
return (1000 + slow_tmr_interval - 1) / slow_tmr_interval;
}

void tcp_pcb_init(struct tcp_pcb *pcb, u8_t prio, void *container)
{
u32_t iss;
Expand All @@ -927,9 +932,10 @@ void tcp_pcb_init(struct tcp_pcb *pcb, u8_t prio, void *container)
pcb->mss = pcb->advtsd_mss;
pcb->user_timeout_ms = 0;
pcb->ticks_since_data_sent = -1;
pcb->rto = 3000 / slow_tmr_interval;
// Set initial RTO to 1 second as per RFC 6298
pcb->rto = get_initial_rto();
pcb->sa = 0;
pcb->sv = 3000 / slow_tmr_interval;
pcb->sv = get_initial_rto();
pcb->rtime = -1;
#if TCP_CC_ALGO_MOD
switch (lwip_cc_algo_module) {
Expand Down Expand Up @@ -985,9 +991,10 @@ void tcp_pcb_recycle(struct tcp_pcb *pcb)
pcb->flags = 0;
pcb->user_timeout_ms = 0;
pcb->ticks_since_data_sent = -1;
pcb->rto = 3000 / slow_tmr_interval;
// Set initial RTO to 1 second as per RFC 6298
pcb->rto = get_initial_rto();
pcb->sa = 0;
pcb->sv = 3000 / slow_tmr_interval;
pcb->sv = get_initial_rto();
pcb->nrtx = 0;
pcb->dupacks = 0;
pcb->rtime = -1;
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20 changes: 20 additions & 0 deletions src/core/util/sys_vars.cpp
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Expand Up @@ -1621,6 +1621,16 @@ void mce_sys_var::get_env_params()
tcp_timer_resolution_msec = timer_resolution_msec;
}

// RFC 1122 Section 4.2.3.2: Delayed ACK timer must not exceed 500ms
// This limits TCP timer resolution to ensure protocol compliance and proper RTO calculations
if (tcp_timer_resolution_msec > 500) {
vlog_printf(VLOG_WARNING,
"TCP timer resolution [%s=%d] exceeds RFC 1122 maximum of 500ms. "
"Clamping to 500ms to ensure protocol compliance.\n",
SYS_VAR_TCP_TIMER_RESOLUTION_MSEC, tcp_timer_resolution_msec);
tcp_timer_resolution_msec = 500;
}

if ((env_ptr = getenv(SYS_VAR_INTERNAL_THREAD_CPUSET))) {
snprintf(internal_thread_cpuset, FILENAME_MAX, "%s", env_ptr);
}
Expand Down Expand Up @@ -2744,6 +2754,16 @@ void mce_sys_var::configure_memory_limits(const config_registry &registry)
tcp_timer_resolution_msec = timer_resolution_msec;
}

// RFC 1122 Section 4.2.3.2: Delayed ACK timer must not exceed 500ms
// This limits TCP timer resolution to ensure protocol compliance and proper RTO calculations
if (tcp_timer_resolution_msec > 500) {
vlog_printf(VLOG_WARNING,
"TCP timer resolution [%s=%d] exceeds RFC 1122 maximum of 500ms. "
"Clamping to 500ms to ensure protocol compliance.\n",
SYS_VAR_TCP_TIMER_RESOLUTION_MSEC, tcp_timer_resolution_msec);
tcp_timer_resolution_msec = 500;
}

if (registry.value_exists("performance.threading.cpuset")) {
snprintf(internal_thread_cpuset, FILENAME_MAX, "%s",
registry.get_value<std::string>("performance.threading.cpuset").c_str());
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