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gianfar: Simplify MQ polling to avoid soft lockup

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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@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Claudiu Manoil 2013-10-14 17:05:09 +03:00 committed by David S. Miller
parent 9877b25382
commit 3ba405db1c
1 changed files with 35 additions and 46 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

81
drivers/net/ethernet/freescale/gianfar.c
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@ -2900,7 +2900,7 @@ 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;
@ -2915,62 +2915,51 @@ 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;
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;
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(&regs->rstat,
RSTAT_CLEAR_RXF0 >> i);
rstat_rxf &= ~(RSTAT_CLEAR_RXF0 >> i);
num_act_queues--;
/* finished processing this queue */
if (work_done_per_q < budget_per_q) {
/* clear active queue hw indication */
gfar_write(&regs->rstat,
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;
}
if (!num_act_queues)
break;
}
}
if (work_done >= budget)
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(&regs->rstat, gfargrp->rstat);
/* Clear the halt bit in RSTAT */
gfar_write(&regs->rstat, gfargrp->rstat);
gfar_write(&regs->imask, IMASK_DEFAULT);
gfar_write(&regs->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;