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Commit 7f6c5539 authored by Guilherme G. Piccoli's avatar Guilherme G. Piccoli Committed by Jeff Kirsher
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i40e: use valid online CPU on q_vector initialization 



Currently, the q_vector initialization routine sets the affinity_mask
of a q_vector based on v_idx value. 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
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.

This patch changes the way q_vector's affinity_mask is created: it iterates
on v_idx, but consumes the CPU index from the cpu_online_mask instead of
just using the v_idx incremental value.

No functional changes were introduced.

Signed-off-by: default avatarGuilherme G Piccoli <gpiccoli@linux.vnet.ibm.com>
Tested-by: default avatarAndrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: default avatarJeff Kirsher <jeffrey.t.kirsher@intel.com>
parent 4b732cd4

drivers/net/ethernet/intel/i40e/i40e_main.c

+11 −5
Original line number Diff line number Diff line
@@ -7721,10 +7721,11 @@ static int i40e_init_msix(struct i40e_pf *pf) 
 * i40e_vsi_alloc_q_vector - Allocate memory for a single interrupt vector

 * @vsi: the VSI being configured

 * @v_idx: index of the vector in the vsi struct

 * @cpu: cpu to be used on affinity_mask

 *

 * We allocate one q_vector.  If allocation fails we return -ENOMEM.

 **/

static int i40e_vsi_alloc_q_vector(struct i40e_vsi *vsi, int v_idx)

static int i40e_vsi_alloc_q_vector(struct i40e_vsi *vsi, int v_idx, int cpu)

{

	struct i40e_q_vector *q_vector;
@@ -7735,7 +7736,8 @@ static int i40e_vsi_alloc_q_vector(struct i40e_vsi *vsi, int v_idx) 


	q_vector->vsi = vsi;

	q_vector->v_idx = v_idx;

	cpumask_set_cpu(v_idx, &q_vector->affinity_mask);

	cpumask_set_cpu(cpu, &q_vector->affinity_mask);



	if (vsi->netdev)

		netif_napi_add(vsi->netdev, &q_vector->napi,

			       i40e_napi_poll, NAPI_POLL_WEIGHT);
@@ -7759,8 +7761,7 @@ static int i40e_vsi_alloc_q_vector(struct i40e_vsi *vsi, int v_idx) 
static int i40e_vsi_alloc_q_vectors(struct i40e_vsi *vsi)

{

	struct i40e_pf *pf = vsi->back;

	int v_idx, num_q_vectors;

	int err;

	int err, v_idx, num_q_vectors, current_cpu;



	/* if not MSIX, give the one vector only to the LAN VSI */

	if (pf->flags & I40E_FLAG_MSIX_ENABLED)
@@ -7770,10 +7771,15 @@ static int i40e_vsi_alloc_q_vectors(struct i40e_vsi *vsi) 
	else

		return -EINVAL;



	current_cpu = cpumask_first(cpu_online_mask);



	for (v_idx = 0; v_idx < num_q_vectors; v_idx++) {

		err = i40e_vsi_alloc_q_vector(vsi, v_idx);

		err = i40e_vsi_alloc_q_vector(vsi, v_idx, current_cpu);

		if (err)

			goto err_out;

		current_cpu = cpumask_next(current_cpu, cpu_online_mask);

		if (unlikely(current_cpu >= nr_cpu_ids))

			current_cpu = cpumask_first(cpu_online_mask);

	}



	return 0;