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Date: Tue, 07 Jun 2011 08:50:03 +0200 From: Eric Dumazet <eric.dumazet@...il.com> To: David Miller <davem@...emloft.net> Cc: heiko.carstens@...ibm.com, blaschka@...ux.vnet.ibm.com, netdev@...r.kernel.org, linux-s390@...r.kernel.org Subject: [PATCH] net: cpu offline cause napi stall From: Heiko Carstens <heiko.carstens@...ibm.com> 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@...ux.vnet.ibm.com> Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com> Tested-by: Eric Dumazet <eric.dumazet@...il.com> --- While doing my tests on bnx2x adapter, I found patch was working ok, but /proc/interrupts still increment interrupt count on my offlined cpu... go figure... net/core/dev.c | 5 +++++ 1 files changed, 5 insertions(+) diff --git a/net/core/dev.c b/net/core/dev.c index 9393078..095909c 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -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(); -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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