From 96eb3d883dde86b8af2748d5932d5c53a35dbb8c Mon Sep 17 00:00:00 2001 From: Felix Fietkau Date: Thu, 27 Feb 2014 23:02:37 +0000 Subject: [PATCH] cns3xxx: ethernet - resolve SMP issue The combination of r35942 and r35952 causes an issue where eth_schedule_poll() can be called from a different CPU between the call to napi_complete() and the setting of cur_index which can break the rx ring accounting and cause ethernet latency and/or ethernet stalls. The issue can be easilly created by adding a couple of artificial delays such as: @@ -715,6 +715,7 @@ static int eth_poll(struct napi_struct *napi, int budget) if (!received) { napi_complete(napi); +udelay(1000); enable_irq(IRQ_CNS3XXX_SW_R0RXC); } @@ -727,6 +728,7 @@ static int eth_poll(struct napi_struct *napi, int budget) rx_ring->cur_index = i; wmb(); +udelay(1000); enable_rx_dma(sw); return received; This patch moves the setting of cur_index back up where it needs to be and addresses the original corner case that r35942 was trying to catch in an improved fashion by checking to see if the rx descriptor ring has become full before interrupts were re-enabled so that a poll can be scheduled again and avoid an rx stall caused by rx interrupts ceasing to fire again. Signed-off-by: Tim Harvey SVN-Revision: 39761 --- .../files/drivers/net/ethernet/cavium/cns3xxx_eth.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/target/linux/cns3xxx/files/drivers/net/ethernet/cavium/cns3xxx_eth.c b/target/linux/cns3xxx/files/drivers/net/ethernet/cavium/cns3xxx_eth.c index db15a2e2e50..bbbbf5c0916 100644 --- a/target/linux/cns3xxx/files/drivers/net/ethernet/cavium/cns3xxx_eth.c +++ b/target/linux/cns3xxx/files/drivers/net/ethernet/cavium/cns3xxx_eth.c @@ -713,9 +713,14 @@ static int eth_poll(struct napi_struct *napi, int budget) } } + rx_ring->cur_index = i; if (!received) { napi_complete(napi); enable_irq(IRQ_CNS3XXX_SW_R0RXC); + + /* if rx descriptors are full schedule another poll */ + if (rx_ring->desc[(i-1) & (RX_DESCS-1)].cown) + eth_schedule_poll(sw); } spin_lock_bh(&tx_lock); @@ -724,8 +729,6 @@ static int eth_poll(struct napi_struct *napi, int budget) cns3xxx_alloc_rx_buf(sw, received); - rx_ring->cur_index = i; - wmb(); enable_rx_dma(sw);