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authorJacob Erlbeck <jerlbeck@sysmocom.de>2015-07-17 16:39:09 +0200
committerJacob Erlbeck <jerlbeck@sysmocom.de>2015-07-21 19:22:36 +0200
commitd4ad731baecb1993481941b0cbb6b6d512708572 (patch)
tree1f2b8ecc13a1dd0462fb4a60187a396b009b377b
parent4f666bc1136eb581d11dc47741928725c76b09c6 (diff)
llc: Use CoDel to drop packages from the LLC queue
Currently packets are only dropped if they have reached their maximum life time. This leads to LLC queues being constantly filled under load, increasing the latency up to the maximum life time. This kind of bufferbloat hinders TCP's congestion avoidance algorithms. To keep the queues short, the CoDel active queue management algorithm can be used. This commit changes to llc_dequeue method to apply the CoDel algorithm to selectively drop LLC frames before they passed to the TBF layer to be encoded in BSNs. This feature is currently disabled by default. The CoDel state is managed per MS since the LLC queues are also kept in the MS objects. Note that there is still some buffering in the TBF objects, in the worst case (CS4) 3.5kByte + LLC-MTU octets are stored there. The resulting additional packet delay is not (yet) taken into account for CoDel. Also note that configuration changes are applied to new MS objects only. The following VTY commands are added to the 'pcu' node: - queue codel activates CoDel, the interval is selected by the implementation - queue codel interval <1-1000> activates CoDel with a fixed interval given in centiseconds (10ms-10s) - no queue codel deactivates CoDel Which interval value to use is still an open issue. For high speed links (e.g. Ethernet), CoDel suggests 100ms. For slower links, the expected RTT is recommended. The current implementation uses a default value of 2000ms. Measurements: Note that the following measurements depend on several other factors, most notably the interaction with the SGSN's flow control. They are just examples to give an idea how CoDel might influence some parameters. The measurements have been done with a single E71, first with a running ping only (Idle), then with an additional TCP download of a 360k file (Busy). The CoDel interval was set to 1s. - Idle : ping ~400ms, avg queue delay 0ms, dropped 0 - Busy, No CoDel: ping ~6s, avg queue delay 4-6s, dropped 0, scheduled 948, duration 54s - Busy, CoDel: ping 500-1500ms, avg queue delay ~600ms, dropped 77, scheduled 1040, duration 60s More measurements with two MS downloading in parallel (two independant measurements per case). - Busy, No CoDel: dropped 0, scheduled 1883, duration 121s dropped 19, scheduled 2003, duration 133s - Busy, CoDel: dropped 22, scheduled 1926, duration 116s dropped 22, scheduled 1955, duration 108s Sponsored-by: On-Waves ehf
-rw-r--r--src/bts.h4
-rw-r--r--src/gprs_ms.cpp18
-rw-r--r--src/gprs_ms.h9
-rw-r--r--src/pcu_vty.c51
-rw-r--r--src/tbf_dl.cpp10
5 files changed, 91 insertions, 1 deletions
diff --git a/src/bts.h b/src/bts.h
index 1a6d259..ec17ef2 100644
--- a/src/bts.h
+++ b/src/bts.h
@@ -36,6 +36,9 @@ extern "C" {
#include <stdint.h>
+#define LLC_CODEL_DISABLE 0
+#define LLC_CODEL_USE_DEFAULT (-1)
+
struct BTS;
struct GprsMs;
@@ -152,6 +155,7 @@ struct gprs_rlcmac_bts {
uint16_t force_llc_lifetime; /* overrides lifetime from SGSN */
uint32_t llc_discard_csec;
uint32_t llc_idle_ack_csec;
+ uint32_t llc_codel_interval_msec; /* 0=disabled, -1=use default interval */
uint8_t t3142;
uint8_t t3169;
uint8_t t3191;
diff --git a/src/gprs_ms.cpp b/src/gprs_ms.cpp
index b36c61d..e0023e3 100644
--- a/src/gprs_ms.cpp
+++ b/src/gprs_ms.cpp
@@ -24,6 +24,7 @@
#include "bts.h"
#include "tbf.h"
#include "gprs_debug.h"
+#include "gprs_codel.h"
#include <time.h>
@@ -32,6 +33,8 @@ extern "C" {
#include <osmocom/core/utils.h>
}
+#define GPRS_CODEL_SLOW_INTERVAL_MS 2000
+
extern void *tall_pcu_ctx;
static int64_t now_msec()
@@ -102,8 +105,11 @@ GprsMs::GprsMs(BTS *bts, uint32_t tlli) :
m_nack_rate_dl(0),
m_reserved_dl_slots(0),
m_reserved_ul_slots(0),
- m_current_trx(NULL)
+ m_current_trx(NULL),
+ m_codel_state(NULL)
{
+ int codel_interval = LLC_CODEL_USE_DEFAULT;
+
LOGP(DRLCMAC, LOGL_INFO, "Creating MS object, TLLI = 0x%08x\n", tlli);
m_imsi[0] = 0;
@@ -118,6 +124,16 @@ GprsMs::GprsMs(BTS *bts, uint32_t tlli) :
m_current_cs_dl = m_bts->bts_data()->initial_cs_dl;
if (m_current_cs_dl < 1)
m_current_cs_dl = 1;
+
+ codel_interval = m_bts->bts_data()->llc_codel_interval_msec;
+ }
+
+ if (codel_interval) {
+ if (codel_interval == LLC_CODEL_USE_DEFAULT)
+ codel_interval = GPRS_CODEL_SLOW_INTERVAL_MS;
+ m_codel_state = talloc(this, struct gprs_codel);
+ gprs_codel_init(m_codel_state);
+ gprs_codel_set_interval(m_codel_state, codel_interval);
}
m_last_cs_not_low = now_msec();
}
diff --git a/src/gprs_ms.h b/src/gprs_ms.h
index 1a135cb..185ffd2 100644
--- a/src/gprs_ms.h
+++ b/src/gprs_ms.h
@@ -23,6 +23,7 @@
struct gprs_rlcmac_tbf;
struct gprs_rlcmac_dl_tbf;
struct gprs_rlcmac_ul_tbf;
+struct gprs_codel;
#include "cxx_linuxlist.h"
#include "llc.h"
@@ -92,6 +93,7 @@ public:
gprs_llc_queue *llc_queue();
const gprs_llc_queue *llc_queue() const;
+ gprs_codel *codel_state() const;
void set_timeout(unsigned secs);
@@ -157,6 +159,8 @@ private:
uint8_t m_reserved_dl_slots;
uint8_t m_reserved_ul_slots;
gprs_rlcmac_trx *m_current_trx;
+
+ struct gprs_codel *m_codel_state;
};
inline uint32_t GprsMs::tlli() const
@@ -207,6 +211,11 @@ inline const gprs_llc_queue *GprsMs::llc_queue() const
return &m_llc_queue;
}
+inline gprs_codel *GprsMs::codel_state() const
+{
+ return m_codel_state;
+}
+
inline unsigned GprsMs::nack_rate_dl() const
{
return m_nack_rate_dl;
diff --git a/src/pcu_vty.c b/src/pcu_vty.c
index ed708f8..94f89b5 100644
--- a/src/pcu_vty.c
+++ b/src/pcu_vty.c
@@ -116,6 +116,14 @@ static int config_write_pcu(struct vty *vty)
if (bts->llc_idle_ack_csec)
vty_out(vty, " queue idle-ack-delay %d%s", bts->llc_idle_ack_csec,
VTY_NEWLINE);
+ if (bts->llc_codel_interval_msec == LLC_CODEL_USE_DEFAULT)
+ vty_out(vty, " queue codel%s", VTY_NEWLINE);
+ else if (bts->llc_codel_interval_msec == LLC_CODEL_DISABLE)
+ vty_out(vty, " no queue codel%s", VTY_NEWLINE);
+ else
+ vty_out(vty, " queue codel interval %d%s",
+ bts->llc_codel_interval_msec/10, VTY_NEWLINE);
+
if (bts->alloc_algorithm == alloc_algorithm_a)
vty_out(vty, " alloc-algorithm a%s", VTY_NEWLINE);
if (bts->alloc_algorithm == alloc_algorithm_b)
@@ -419,6 +427,46 @@ DEFUN(cfg_pcu_no_queue_hysteresis,
return CMD_SUCCESS;
}
+#define QUEUE_CODEL_STR "Set CoDel queue management\n"
+
+DEFUN(cfg_pcu_queue_codel,
+ cfg_pcu_queue_codel_cmd,
+ "queue codel",
+ QUEUE_STR QUEUE_CODEL_STR)
+{
+ struct gprs_rlcmac_bts *bts = bts_main_data();
+
+ bts->llc_codel_interval_msec = LLC_CODEL_USE_DEFAULT;
+
+ return CMD_SUCCESS;
+}
+
+DEFUN(cfg_pcu_queue_codel_interval,
+ cfg_pcu_queue_codel_interval_cmd,
+ "queue codel interval <1-1000>",
+ QUEUE_STR QUEUE_CODEL_STR "Specify interval\n" "Interval in centi-seconds")
+{
+ struct gprs_rlcmac_bts *bts = bts_main_data();
+ uint16_t csec = atoi(argv[0]);
+
+ bts->llc_codel_interval_msec = 10*csec;
+
+ return CMD_SUCCESS;
+}
+
+DEFUN(cfg_pcu_no_queue_codel,
+ cfg_pcu_no_queue_codel_cmd,
+ "no queue codel",
+ NO_STR QUEUE_STR QUEUE_CODEL_STR)
+{
+ struct gprs_rlcmac_bts *bts = bts_main_data();
+
+ bts->llc_codel_interval_msec = LLC_CODEL_DISABLE;
+
+ return CMD_SUCCESS;
+}
+
+
#define QUEUE_IDLE_ACK_STR "Request an ACK after the last DL LLC frame in centi-seconds\n"
DEFUN(cfg_pcu_queue_idle_ack_delay,
@@ -776,6 +824,9 @@ int pcu_vty_init(const struct log_info *cat)
install_element(PCU_NODE, &cfg_pcu_no_queue_lifetime_cmd);
install_element(PCU_NODE, &cfg_pcu_queue_hysteresis_cmd);
install_element(PCU_NODE, &cfg_pcu_no_queue_hysteresis_cmd);
+ install_element(PCU_NODE, &cfg_pcu_queue_codel_cmd);
+ install_element(PCU_NODE, &cfg_pcu_queue_codel_interval_cmd);
+ install_element(PCU_NODE, &cfg_pcu_no_queue_codel_cmd);
install_element(PCU_NODE, &cfg_pcu_queue_idle_ack_delay_cmd);
install_element(PCU_NODE, &cfg_pcu_no_queue_idle_ack_delay_cmd);
install_element(PCU_NODE, &cfg_pcu_alloc_cmd);
diff --git a/src/tbf_dl.cpp b/src/tbf_dl.cpp
index cdd02ba..4739a50 100644
--- a/src/tbf_dl.cpp
+++ b/src/tbf_dl.cpp
@@ -25,6 +25,7 @@
#include <gprs_rlcmac.h>
#include <gprs_debug.h>
#include <gprs_bssgp_pcu.h>
+#include <gprs_codel.h>
#include <decoding.h>
#include "pcu_utils.h"
@@ -36,6 +37,7 @@ extern "C" {
#include <errno.h>
#include <string.h>
+#include <math.h>
/* After sending these frames, we poll for ack/nack. */
#define POLL_ACK_AFTER_FRAMES 20
@@ -249,6 +251,13 @@ struct msgb *gprs_rlcmac_dl_tbf::llc_dequeue(bssgp_bvc_ctx *bctx)
gprs_bssgp_update_queue_delay(tv_recv, &tv_now);
+ if (ms() && ms()->codel_state()) {
+ int bytes = llc_queue()->octets();
+ if (gprs_codel_control(ms()->codel_state(),
+ tv_recv, &tv_now, bytes))
+ goto drop_frame;
+ }
+
/* Is the age below the low water mark? */
if (!gprs_llc_queue::is_frame_expired(&tv_now2, tv_disc))
break;
@@ -274,6 +283,7 @@ struct msgb *gprs_rlcmac_dl_tbf::llc_dequeue(bssgp_bvc_ctx *bctx)
}
bts->llc_timedout_frame();
+drop_frame:
frames++;
octets += msg->len;
msgb_free(msg);