From 6d9777298b54bf1212fcaa6ee6679a430ceca452 Mon Sep 17 00:00:00 2001 From: Jacob Keller Date: Fri, 14 Jul 2017 09:10:11 -0400 Subject: [PATCH] i40e: invert logic for checking incorrect cpu vs irq affinity In commit 96db776a3682 ("i40e/vf: fix interrupt affinity bug") we added some code to force exit of polling in case we did not have the correct CPU. This is important since it was possible for the IRQ affinity to be changed while the CPU is pegged at 100%. This can result in the polling routine being stuck on the wrong CPU until traffic finally stops. Unfortunately, the implementation, "if the CPU is correct, exit as normal, otherwise, fall-through to the end-polling exit" is incredibly confusing to reason about. In this case, the normal flow looks like the exception, while the exception actually occurs far away from the if statement and comment. We recently discovered and fixed a bug in this code because we were incorrectly initializing the affinity mask. Re-write the code so that the exceptional case is handled at the check, rather than having the logic be spread through the regular exit flow. This does end up with minor code duplication, but the resulting code is much easier to reason about. The new logic is identical, but inverted. If we are running on a CPU not in our affinity mask, we'll exit polling. However, the code flow is much easier to understand. Note that we don't actually have to check for MSI-X, because in the MSI case we'll only have one q_vector, but its default affinity mask should be correct as it includes all CPUs when it's initialized. Further, we could at some point add code to setup the notifier for the non-MSI-X case and enable this workaround for that case too, if desired, though there isn't much gain since its unlikely to be the common case. Signed-off-by: Jacob Keller Tested-by: Andrew Bowers Signed-off-by: Jeff Kirsher --- drivers/net/ethernet/intel/i40e/i40e_txrx.c | 31 +++++++++---------- drivers/net/ethernet/intel/i40evf/i40e_txrx.c | 30 +++++++++--------- 2 files changed, 30 insertions(+), 31 deletions(-) diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c index 5c1edcce9459..3999afea518b 100644 --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c @@ -2369,7 +2369,6 @@ int i40e_napi_poll(struct napi_struct *napi, int budget) /* If work not completed, return budget and polling will return */ if (!clean_complete) { - const cpumask_t *aff_mask = &q_vector->affinity_mask; int cpu_id = smp_processor_id(); /* It is possible that the interrupt affinity has changed but, @@ -2379,15 +2378,22 @@ int i40e_napi_poll(struct napi_struct *napi, int budget) * continue to poll, otherwise we must stop polling so the * interrupt can move to the correct cpu. */ - if (likely(cpumask_test_cpu(cpu_id, aff_mask) || - !(vsi->back->flags & I40E_FLAG_MSIX_ENABLED))) { + if (!cpumask_test_cpu(cpu_id, &q_vector->affinity_mask)) { + /* Tell napi that we are done polling */ + napi_complete_done(napi, work_done); + + /* Force an interrupt */ + i40e_force_wb(vsi, q_vector); + + /* Return budget-1 so that polling stops */ + return budget - 1; + } tx_only: - if (arm_wb) { - q_vector->tx.ring[0].tx_stats.tx_force_wb++; - i40e_enable_wb_on_itr(vsi, q_vector); - } - return budget; + if (arm_wb) { + q_vector->tx.ring[0].tx_stats.tx_force_wb++; + i40e_enable_wb_on_itr(vsi, q_vector); } + return budget; } if (vsi->back->flags & I40E_TXR_FLAGS_WB_ON_ITR) @@ -2396,14 +2402,7 @@ tx_only: /* Work is done so exit the polling mode and re-enable the interrupt */ napi_complete_done(napi, work_done); - /* If we're prematurely stopping polling to fix the interrupt - * affinity we want to make sure polling starts back up so we - * issue a call to i40e_force_wb which triggers a SW interrupt. - */ - if (!clean_complete) - i40e_force_wb(vsi, q_vector); - else - i40e_update_enable_itr(vsi, q_vector); + i40e_update_enable_itr(vsi, q_vector); return min(work_done, budget - 1); } diff --git a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c b/drivers/net/ethernet/intel/i40evf/i40e_txrx.c index d91676ccf125..f15e341ada9e 100644 --- a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c +++ b/drivers/net/ethernet/intel/i40evf/i40e_txrx.c @@ -1575,7 +1575,6 @@ int i40evf_napi_poll(struct napi_struct *napi, int budget) /* If work not completed, return budget and polling will return */ if (!clean_complete) { - const cpumask_t *aff_mask = &q_vector->affinity_mask; int cpu_id = smp_processor_id(); /* It is possible that the interrupt affinity has changed but, @@ -1585,14 +1584,22 @@ int i40evf_napi_poll(struct napi_struct *napi, int budget) * continue to poll, otherwise we must stop polling so the * interrupt can move to the correct cpu. */ - if (likely(cpumask_test_cpu(cpu_id, aff_mask))) { + if (!cpumask_test_cpu(cpu_id, &q_vector->affinity_mask)) { + /* Tell napi that we are done polling */ + napi_complete_done(napi, work_done); + + /* Force an interrupt */ + i40evf_force_wb(vsi, q_vector); + + /* Return budget-1 so that polling stops */ + return budget - 1; + } tx_only: - if (arm_wb) { - q_vector->tx.ring[0].tx_stats.tx_force_wb++; - i40e_enable_wb_on_itr(vsi, q_vector); - } - return budget; + if (arm_wb) { + q_vector->tx.ring[0].tx_stats.tx_force_wb++; + i40e_enable_wb_on_itr(vsi, q_vector); } + return budget; } if (vsi->back->flags & I40E_TXR_FLAGS_WB_ON_ITR) @@ -1601,14 +1608,7 @@ tx_only: /* Work is done so exit the polling mode and re-enable the interrupt */ napi_complete_done(napi, work_done); - /* If we're prematurely stopping polling to fix the interrupt - * affinity we want to make sure polling starts back up so we - * issue a call to i40evf_force_wb which triggers a SW interrupt. - */ - if (!clean_complete) - i40evf_force_wb(vsi, q_vector); - else - i40e_update_enable_itr(vsi, q_vector); + i40e_update_enable_itr(vsi, q_vector); return min(work_done, budget - 1); } -- 2.20.1