Commit 264524d5 authored Jun 06, 2011 by Heiko Carstens Committed by David S. Miller Jun 07, 2011

net: cpu offline cause napi stall



Frank Blaschka reported :
<quote>
  During heavy network load we turn off/on cpus.
  Sometimes this causes a stall on the network device.
  Digging into the dump I found out following:

  napi is scheduled but does not run. From the I/O buffers
  and the napi state I see napi/rx_softirq processing has stopped
  because the budget was reached. napi stays in the
  softnet_data poll_list and the rx_softirq was raised again.

  I assume at this time the cpu offline comes in,
  the rx softirq is raised/moved to another cpu but napi stays in the
  poll_list of the softnet_data of the now offline cpu.

  Reviewing dev_cpu_callback (net/core/dev.c) I did not find the
  poll_list is transfered to the new cpu.
</quote>

This patch is a straightforward implementation of Frank suggestion :

Transfert poll_list and trigger NET_RX_SOFTIRQ on new cpu.

Reported-by: Frank Blaschka <blaschka@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Tested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 6407d74c

net/core/dev.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -6178,6 +6178,11 @@ static int dev_cpu_callback(struct notifier_block *nfb,
		oldsd->output_queue = NULL;
		oldsd->output_queue_tailp = &oldsd->output_queue;
		}
		/* Append NAPI poll list from offline CPU. */
		if (!list_empty(&oldsd->poll_list)) {
		list_splice_init(&oldsd->poll_list, &sd->poll_list);
		raise_softirq_irqoff(NET_RX_SOFTIRQ);
		}

		raise_softirq_irqoff(NET_TX_SOFTIRQ);
		local_irq_enable();

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