This is a note to let you know that I've just added the patch titled
i40e/i40evf: spread CPU affinity hints across online CPUs only
to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: i40e-i40evf-spread-cpu-affinity-hints-across-online-cpus-only.patch and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Wed Dec 20 18:17:52 CET 2017
From: Jacob Keller jacob.e.keller@intel.com Date: Tue, 29 Aug 2017 05:32:31 -0400 Subject: i40e/i40evf: spread CPU affinity hints across online CPUs only
From: Jacob Keller jacob.e.keller@intel.com
[ Upstream commit be664cbefc50977aaefc868ba6a1109ec9b7449d ]
Currently, when setting up the IRQ for a q_vector, we set an affinity hint based on the v_idx of that q_vector. Meaning a loop iterates on v_idx, which is an incremental value, and the cpumask is created based on this value.
This is a problem in systems with multiple logical CPUs per core (like in simultaneous multithreading (SMT) scenarios). If we disable some logical CPUs, by turning SMT off for example, we will end up with a sparse cpu_online_mask, i.e., only the first CPU in a core is online, and incremental filling in q_vector cpumask might lead to multiple offline CPUs being assigned to q_vectors.
Example: if we have a system with 8 cores each one containing 8 logical CPUs (SMT == 8 in this case), we have 64 CPUs in total. But if SMT is disabled, only the 1st CPU in each core remains online, so the cpu_online_mask in this case would have only 8 bits set, in a sparse way.
In general case, when SMT is off the cpu_online_mask has only C bits set: 0, 1*N, 2*N, ..., C*(N-1) where C == # of cores; N == # of logical CPUs per core. In our example, only bits 0, 8, 16, 24, 32, 40, 48, 56 would be set.
Instead, we should only assign hints for CPUs which are online. Even better, the kernel already provides a function, cpumask_local_spread() which takes an index and returns a CPU, spreading the interrupts across local NUMA nodes first, and then remote ones if necessary.
Since we generally have a 1:1 mapping between vectors and CPUs, there is no real advantage to spreading vectors to local CPUs first. In order to avoid mismatch of the default XPS hints, we'll pass -1 so that it spreads across all CPUs without regard to the node locality.
Note that we don't need to change the q_vector->affinity_mask as this is initialized to cpu_possible_mask, until an actual affinity is set and then notified back to us.
Signed-off-by: Jacob Keller jacob.e.keller@intel.com Tested-by: Andrew Bowers andrewx.bowers@intel.com Signed-off-by: Jeff Kirsher jeffrey.t.kirsher@intel.com Signed-off-by: Sasha Levin alexander.levin@verizon.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/ethernet/intel/i40e/i40e_main.c | 16 +++++++++++----- drivers/net/ethernet/intel/i40evf/i40evf_main.c | 9 ++++++--- 2 files changed, 17 insertions(+), 8 deletions(-)
--- a/drivers/net/ethernet/intel/i40e/i40e_main.c +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c @@ -2874,14 +2874,15 @@ static void i40e_vsi_free_rx_resources(s static void i40e_config_xps_tx_ring(struct i40e_ring *ring) { struct i40e_vsi *vsi = ring->vsi; + int cpu;
if (!ring->q_vector || !ring->netdev) return;
if ((vsi->tc_config.numtc <= 1) && !test_and_set_bit(__I40E_TX_XPS_INIT_DONE, &ring->state)) { - netif_set_xps_queue(ring->netdev, - get_cpu_mask(ring->q_vector->v_idx), + cpu = cpumask_local_spread(ring->q_vector->v_idx, -1); + netif_set_xps_queue(ring->netdev, get_cpu_mask(cpu), ring->queue_index); }
@@ -3471,6 +3472,7 @@ static int i40e_vsi_request_irq_msix(str int tx_int_idx = 0; int vector, err; int irq_num; + int cpu;
for (vector = 0; vector < q_vectors; vector++) { struct i40e_q_vector *q_vector = vsi->q_vectors[vector]; @@ -3506,10 +3508,14 @@ static int i40e_vsi_request_irq_msix(str q_vector->affinity_notify.notify = i40e_irq_affinity_notify; q_vector->affinity_notify.release = i40e_irq_affinity_release; irq_set_affinity_notifier(irq_num, &q_vector->affinity_notify); - /* get_cpu_mask returns a static constant mask with - * a permanent lifetime so it's ok to use here. + /* Spread affinity hints out across online CPUs. + * + * get_cpu_mask returns a static constant mask with + * a permanent lifetime so it's ok to pass to + * irq_set_affinity_hint without making a copy. */ - irq_set_affinity_hint(irq_num, get_cpu_mask(q_vector->v_idx)); + cpu = cpumask_local_spread(q_vector->v_idx, -1); + irq_set_affinity_hint(irq_num, get_cpu_mask(cpu)); }
vsi->irqs_ready = true; --- a/drivers/net/ethernet/intel/i40evf/i40evf_main.c +++ b/drivers/net/ethernet/intel/i40evf/i40evf_main.c @@ -546,6 +546,7 @@ i40evf_request_traffic_irqs(struct i40ev unsigned int vector, q_vectors; unsigned int rx_int_idx = 0, tx_int_idx = 0; int irq_num, err; + int cpu;
i40evf_irq_disable(adapter); /* Decrement for Other and TCP Timer vectors */ @@ -584,10 +585,12 @@ i40evf_request_traffic_irqs(struct i40ev q_vector->affinity_notify.release = i40evf_irq_affinity_release; irq_set_affinity_notifier(irq_num, &q_vector->affinity_notify); - /* get_cpu_mask returns a static constant mask with - * a permanent lifetime so it's ok to use here. + /* Spread the IRQ affinity hints across online CPUs. Note that + * get_cpu_mask returns a mask with a permanent lifetime so + * it's safe to use as a hint for irq_set_affinity_hint. */ - irq_set_affinity_hint(irq_num, get_cpu_mask(q_vector->v_idx)); + cpu = cpumask_local_spread(q_vector->v_idx, -1); + irq_set_affinity_hint(irq_num, get_cpu_mask(cpu)); }
return 0;
Patches currently in stable-queue which might be from jacob.e.keller@intel.com are
queue-4.14/fm10k-fix-mis-ordered-parameters-in-declaration-for-.ndo_set_vf_bw.patch queue-4.14/fm10k-ensure-we-process-sm-mbx-when-processing-vf-mbx.patch queue-4.14/i40e-i40evf-spread-cpu-affinity-hints-across-online-cpus-only.patch