On Wed, 14 Nov 2001, Andrea Arcangeli wrote:
> > Using the RS232 cable, I get TCP throughput of around 3.6KB/s
> > (28.8Kb/s). Using IrDA with an identical setup (and phone
> > position) I get only 1.2KB/s. I've tried all the obvious things
> > like changing the distance between the Ir sensors etc.
>
> the latency is horrible for me too (order of seconds), but never tried
> without irda stack in the middle (I simply don't have the cable :).
>
> There seems to be some huge packet loss here too. However I never
Ok. Despite not having a T39 it seems my first guess with the MIR problem
was a hit - so lets go for another one:
>From the other guy's report I've seen the T39m announces it would announce
min turn time =0 (or more, of course). While this is perfectly legal from
IrLAP protocol it would mean our stack is granted to start transmission
immediately after the phone finished transmitting, i.e. without applying
any delay to let the T39 receiver recover from saturation. Concerns me
somewhat whether this would be what the specs for the transceiver say.
In most cases the transceiver need some time to recover (1-5 msecs for
most standard devices I've seen). If this fails the first packet to the
phone would arrive while it's still saturated and gets lost. Our stack is
then required to wait up to 500 msec before retry - would IMHO perfectly
explain the bad performance.
So, if you like, lets try to confirm (or rule out) this: The patch below
adds sysctl net.irda.min_tx_turn_time and uses this is a lower limit for
the turn time delay to be used for the other end. Hence setting
/proc/sys/net/irda/min_tx_turn_time to 1000 or 5000 (usec) forces the irda
stack to overrule the pretty optimistic value from the T39m.
Any improvement detectable with this?
Martin
------------------------------
diff -ur linux-2.4.14/net/irda/irsysctl.c v2.4.14-md/net/irda/irsysctl.c
--- linux-2.4.14/net/irda/irsysctl.c Sun Sep 30 15:55:37 2001
+++ v2.4.14-md/net/irda/irsysctl.c Thu Nov 15 20:12:21 2001
@@ -33,7 +33,8 @@
#define NET_IRDA 412 /* Random number */
enum { DISCOVERY=1, DEVNAME, DEBUG, SLOTS, DISCOVERY_TIMEOUT,
- SLOT_TIMEOUT, MAX_BAUD_RATE, MAX_INACTIVE_TIME, LAP_KEEPALIVE_TIME, };
+ SLOT_TIMEOUT, MAX_BAUD_RATE, MAX_INACTIVE_TIME, LAP_KEEPALIVE_TIME,
+ MIN_TX_TURN_TIME };
extern int sysctl_discovery;
extern int sysctl_discovery_slots;
@@ -45,6 +46,7 @@
extern int sysctl_max_baud_rate;
extern int sysctl_max_inactive_time;
extern int sysctl_lap_keepalive_time;
+extern unsigned sysctl_min_tx_turn_time;
#ifdef CONFIG_IRDA_DEBUG
extern unsigned int irda_debug;
@@ -92,6 +94,8 @@
sizeof(int), 0644, NULL, &proc_dointvec },
{ LAP_KEEPALIVE_TIME, "lap_keepalive_time", &sysctl_lap_keepalive_time,
sizeof(int), 0644, NULL, &proc_dointvec },
+ { MIN_TX_TURN_TIME, "min_tx_turn_time", &sysctl_min_tx_turn_time,
+ sizeof(unsigned), 0644, NULL, &proc_doulongvec_minmax },
{ 0 }
};
diff -ur linux-2.4.14/net/irda/qos.c v2.4.14-md/net/irda/qos.c
--- linux-2.4.14/net/irda/qos.c Sat Aug 4 13:24:16 2001
+++ v2.4.14-md/net/irda/qos.c Thu Nov 15 20:21:22 2001
@@ -51,6 +51,14 @@
* Remember that the threshold time (early warning) is fixed to 3s...
*/
int sysctl_max_inactive_time = 12;
+/*
+ * Minimum turn time to be applied before transmitting to the peer.
+ * Nonzero values (usec) are used as lower limit to the per-connection
+ * mtt value which was announced by the other end during negotiation.
+ * Might be helpful if the peer device provides too short mtt.
+ * Default is 0 which means using the unmodified value given by the peer.
+ */
+unsigned sysctl_min_tx_turn_time = 0;
static int irlap_param_baud_rate(void *instance, irda_param_t *param, int get);
static int irlap_param_link_disconnect(void *instance, irda_param_t *parm,
@@ -280,6 +288,23 @@
int index;
IRDA_DEBUG(2, __FUNCTION__ "()\n");
+
+ if (sysctl_min_tx_turn_time > qos->min_turn_time.value) {
+ u8 bits;
+
+ bits = 0x80; /* type 1 parameter - only MSB set */
+ for (index = 0; index <
+sizeof(min_turn_times)/sizeof(*min_turn_times); index++) {
+ if (sysctl_min_tx_turn_time >= min_turn_times[index])
+ break;
+ bits >>= 1;
+ }
+ if (!bits)
+ bits = 0x01; /* IrLAP: max. mtt 10ms */
+
+ sysctl_min_tx_turn_time = min_turn_times[index]; /* adjust to official
+value */
+ qos->min_turn_time.bits = bits;
+ qos->min_turn_time.value = min_turn_times[index];
+ }
/*
* Not allowed to use a max turn time less than 500 ms if the baudrate
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