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Date: Mon, 14 Oct 2013 17:05:09 +0300
From: Claudiu Manoil <claudiu.manoil@...escale.com>
To: <netdev@...r.kernel.org>
CC: "David S. Miller" <davem@...emloft.net>
Subject: [PATCH][net-next] gianfar: Simplify MQ polling to avoid soft lockup
Under certain low traffic conditions, the single core
devices with multiple Rx/Tx queues (MQ mode) may reach
soft lockup due to gfar_poll not returning in proper time.
The following exception was obtained using iperf on a 100Mbit
half-duplex link, for a p1010 single core device:
BUG: soft lockup - CPU#0 stuck for 23s! [iperf:2847]
Modules linked in:
CPU: 0 PID: 2847 Comm: iperf Not tainted 3.12.0-rc3 #16
task: e8bf8000 ti: eeb16000 task.ti: ee646000
NIP: c0255b6c LR: c0367ae8 CTR: c0461c18
REGS: eeb17e70 TRAP: 0901 Not tainted (3.12.0-rc3)
MSR: 00029000 <CE,EE,ME> CR: 44228428 XER: 20000000
GPR00: c0367ad4 eeb17f20 e8bf8000 ee01f4b4 00000008 ffffffff ffffffff
00000000
GPR08: 000000c0 00000008 000000ff ffffffc0 000193fe
NIP [c0255b6c] find_next_bit+0xb8/0xc4
LR [c0367ae8] gfar_poll+0xc8/0x1d8
Call Trace:
[eeb17f20] [c0367ad4] gfar_poll+0xb4/0x1d8 (unreliable)
[eeb17f70] [c0422100] net_rx_action+0xa4/0x158
[eeb17fa0] [c003ec6c] __do_softirq+0xcc/0x17c
[eeb17ff0] [c000c28c] call_do_softirq+0x24/0x3c
[ee647cc0] [c0004660] do_softirq+0x6c/0x94
[ee647ce0] [c003eb9c] local_bh_enable+0x9c/0xa0
[ee647cf0] [c0454fe8] tcp_prequeue_process+0xa4/0xdc
[ee647d10] [c0457e44] tcp_recvmsg+0x498/0x96c
[ee647d80] [c047b630] inet_recvmsg+0x40/0x64
[ee647da0] [c040ca8c] sock_recvmsg+0x90/0xc0
[ee647e30] [c040edb8] SyS_recvfrom+0x98/0xfc
To prevent this, the outer while() loop has been removed
allowing gfar_poll() to return faster even if there's
still budget left. Also, there's no need to recompute
the budget per Rx queue anymore.
Signed-off-by: Claudiu Manoil <claudiu.manoil@...escale.com>
---
drivers/net/ethernet/freescale/gianfar.c | 87 ++++++++++++++------------------
1 file changed, 38 insertions(+), 49 deletions(-)
diff --git a/drivers/net/ethernet/freescale/gianfar.c b/drivers/net/ethernet/freescale/gianfar.c
index 9fbe4dd..d6d810c 100644
--- a/drivers/net/ethernet/freescale/gianfar.c
+++ b/drivers/net/ethernet/freescale/gianfar.c
@@ -2918,7 +2918,7 @@ static int gfar_poll(struct napi_struct *napi, int budget)
struct gfar_priv_rx_q *rx_queue = NULL;
int work_done = 0, work_done_per_q = 0;
int i, budget_per_q = 0;
- int has_tx_work;
+ int has_tx_work = 0;
unsigned long rstat_rxf;
int num_act_queues;
@@ -2933,62 +2933,51 @@ static int gfar_poll(struct napi_struct *napi, int budget)
if (num_act_queues)
budget_per_q = budget/num_act_queues;
- while (1) {
- has_tx_work = 0;
- for_each_set_bit(i, &gfargrp->tx_bit_map, priv->num_tx_queues) {
- tx_queue = priv->tx_queue[i];
- /* run Tx cleanup to completion */
- if (tx_queue->tx_skbuff[tx_queue->skb_dirtytx]) {
- gfar_clean_tx_ring(tx_queue);
- has_tx_work = 1;
- }
+ for_each_set_bit(i, &gfargrp->tx_bit_map, priv->num_tx_queues) {
+ tx_queue = priv->tx_queue[i];
+ /* run Tx cleanup to completion */
+ if (tx_queue->tx_skbuff[tx_queue->skb_dirtytx]) {
+ gfar_clean_tx_ring(tx_queue);
+ has_tx_work = 1;
}
+ }
- for_each_set_bit(i, &gfargrp->rx_bit_map, priv->num_rx_queues) {
- /* skip queue if not active */
- if (!(rstat_rxf & (RSTAT_CLEAR_RXF0 >> i)))
- continue;
-
- rx_queue = priv->rx_queue[i];
- work_done_per_q =
- gfar_clean_rx_ring(rx_queue, budget_per_q);
- work_done += work_done_per_q;
-
- /* finished processing this queue */
- if (work_done_per_q < budget_per_q) {
- /* clear active queue hw indication */
- gfar_write(®s->rstat,
- RSTAT_CLEAR_RXF0 >> i);
- rstat_rxf &= ~(RSTAT_CLEAR_RXF0 >> i);
- num_act_queues--;
-
- if (!num_act_queues)
- break;
- /* recompute budget per Rx queue */
- budget_per_q =
- (budget - work_done) / num_act_queues;
- }
- }
+ for_each_set_bit(i, &gfargrp->rx_bit_map, priv->num_rx_queues) {
+ /* skip queue if not active */
+ if (!(rstat_rxf & (RSTAT_CLEAR_RXF0 >> i)))
+ continue;
- if (work_done >= budget)
- break;
+ rx_queue = priv->rx_queue[i];
+ work_done_per_q =
+ gfar_clean_rx_ring(rx_queue, budget_per_q);
+ work_done += work_done_per_q;
+
+ /* finished processing this queue */
+ if (work_done_per_q < budget_per_q) {
+ /* clear active queue hw indication */
+ gfar_write(®s->rstat,
+ RSTAT_CLEAR_RXF0 >> i);
+ num_act_queues--;
+
+ if (!num_act_queues)
+ break;
+ }
+ }
- if (!num_act_queues && !has_tx_work) {
+ if (!num_act_queues && !has_tx_work) {
- napi_complete(napi);
+ napi_complete(napi);
- /* Clear the halt bit in RSTAT */
- gfar_write(®s->rstat, gfargrp->rstat);
+ /* Clear the halt bit in RSTAT */
+ gfar_write(®s->rstat, gfargrp->rstat);
- gfar_write(®s->imask, IMASK_DEFAULT);
+ gfar_write(®s->imask, IMASK_DEFAULT);
- /* If we are coalescing interrupts, update the timer
- * Otherwise, clear it
- */
- gfar_configure_coalescing(priv, gfargrp->rx_bit_map,
- gfargrp->tx_bit_map);
- break;
- }
+ /* If we are coalescing interrupts, update the timer
+ * Otherwise, clear it
+ */
+ gfar_configure_coalescing(priv, gfargrp->rx_bit_map,
+ gfargrp->tx_bit_map);
}
return work_done;
--
1.7.11.7
--
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