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/*
* Copyright (C) 2006 Michael Brown <mbrown@fensystems.co.uk>.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
FILE_LICENCE ( GPL2_OR_LATER );
#include <stddef.h>
#include <ipxe/timer.h>
#include <ipxe/list.h>
#include <ipxe/process.h>
#include <ipxe/init.h>
#include <ipxe/retry.h>
/** @file
*
* Retry timers
*
* A retry timer is a binary exponential backoff timer. It can be
* used to build automatic retransmission into network protocols.
*
* This implementation of the timer is designed to satisfy RFC 2988
* and therefore be usable as a TCP retransmission timer.
*
*
*/
/* The theoretical minimum that the algorithm in stop_timer() can
* adjust the timeout back down to is seven ticks, so set the minimum
* timeout to at least that value for the sake of consistency.
*/
#define MIN_TIMEOUT 7
/** List of running timers */
static LIST_HEAD ( timers );
/**
* Start timer
*
* @v timer Retry timer
*
* This starts the timer running with the current timeout value. If
* stop_timer() is not called before the timer expires, the timer will
* be stopped and the timer's callback function will be called.
*/
void start_timer ( struct retry_timer *timer ) {
if ( ! timer->running ) {
list_add ( &timer->list, &timers );
ref_get ( timer->refcnt );
}
timer->start = currticks();
timer->running = 1;
/* 0 means "use default timeout" */
if ( timer->min_timeout == 0 )
timer->min_timeout = DEFAULT_MIN_TIMEOUT;
/* We must never be less than MIN_TIMEOUT under any circumstances */
if ( timer->min_timeout < MIN_TIMEOUT )
timer->min_timeout = MIN_TIMEOUT;
/* Honor user-specified minimum timeout */
if ( timer->timeout < timer->min_timeout )
timer->timeout = timer->min_timeout;
DBG2 ( "Timer %p started at time %ld (expires at %ld)\n",
timer, timer->start, ( timer->start + timer->timeout ) );
}
/**
* Start timer with a specified fixed timeout
*
* @v timer Retry timer
* @v timeout Timeout, in ticks
*/
void start_timer_fixed ( struct retry_timer *timer, unsigned long timeout ) {
start_timer ( timer );
timer->timeout = timeout;
DBG2 ( "Timer %p expiry time changed to %ld\n",
timer, ( timer->start + timer->timeout ) );
}
/**
* Stop timer
*
* @v timer Retry timer
*
* This stops the timer and updates the timer's timeout value.
*/
void stop_timer ( struct retry_timer *timer ) {
unsigned long old_timeout = timer->timeout;
unsigned long now = currticks();
unsigned long runtime;
/* If timer was already stopped, do nothing */
if ( ! timer->running )
return;
list_del ( &timer->list );
runtime = ( now - timer->start );
timer->running = 0;
DBG2 ( "Timer %p stopped at time %ld (ran for %ld)\n",
timer, now, runtime );
/* Update timer. Variables are:
*
* r = round-trip time estimate (i.e. runtime)
* t = timeout value (i.e. timer->timeout)
* s = smoothed round-trip time
*
* By choice, we set t = 4s, i.e. allow for four times the
* normal round-trip time to pass before retransmitting.
*
* We want to smooth according to s := ( 7 s + r ) / 8
*
* Since we don't actually store s, this reduces to
* t := ( 7 t / 8 ) + ( r / 2 )
*
*/
if ( timer->count ) {
timer->count--;
} else {
timer->timeout -= ( timer->timeout >> 3 );
timer->timeout += ( runtime >> 1 );
if ( timer->timeout != old_timeout ) {
DBG ( "Timer %p timeout updated to %ld\n",
timer, timer->timeout );
}
}
ref_put ( timer->refcnt );
}
/**
* Handle expired timer
*
* @v timer Retry timer
*/
static void timer_expired ( struct retry_timer *timer ) {
int fail;
/* Stop timer without performing RTT calculations */
DBG2 ( "Timer %p stopped at time %ld on expiry\n",
timer, currticks() );
assert ( timer->running );
list_del ( &timer->list );
timer->running = 0;
timer->count++;
/* Back off the timeout value */
timer->timeout <<= 1;
if ( timer->max_timeout == 0 ) /* 0 means "use default timeout" */
timer->max_timeout = DEFAULT_MAX_TIMEOUT;
if ( ( fail = ( timer->timeout > timer->max_timeout ) ) )
timer->timeout = timer->max_timeout;
DBG ( "Timer %p timeout backed off to %ld\n",
timer, timer->timeout );
/* Call expiry callback */
timer->expired ( timer, fail );
ref_put ( timer->refcnt );
}
/**
* Single-step the retry timer list
*
* @v process Retry timer process
*/
static void retry_step ( struct process *process __unused ) {
struct retry_timer *timer;
unsigned long now = currticks();
unsigned long used;
/* Process at most one timer expiry. We cannot process
* multiple expiries in one pass, because one timer expiring
* may end up triggering another timer's deletion from the
* list.
*/
list_for_each_entry ( timer, &timers, list ) {
used = ( now - timer->start );
if ( used >= timer->timeout ) {
timer_expired ( timer );
break;
}
}
}
/** Retry timer process */
struct process retry_process __permanent_process = {
.list = LIST_HEAD_INIT ( retry_process.list ),
.step = retry_step,
};
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