APPLIED: [PATCH][SRU][Xenial] i40e: use valid online CPU on q_vector initialization

[Thadeu Lima de Souza Cascardo]

On Wed, Jul 12, 2017 at 11:11:06AM +0200, Stefan Bader wrote:
> On 11.07.2017 20:58, Guilherme G. Piccoli wrote:
> > BugLink: https://bugs.launchpad.net/bugs/1703663
> > 
> > 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: Guilherme G Piccoli <gpiccoli at linux.vnet.ibm.com>
> > Tested-by: Andrew Bowers <andrewx.bowers at intel.com>
> > Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher at intel.com>
> 
> > (cherry picked from commit 7f6c553902bfa1c4e3f6cfa955c5ea036c7fe8e4)
> Signed-off-by: Guilherme G Piccoli <gpiccoli at linux.vnet.ibm.com>
> Acked-by: Stefan Bader <stefan.bader at canonical.com>

His Sign-off is already there.

Applied to xenial master-next branch.

Thanks.
Cascardo.

> 
> > ---
> >  drivers/net/ethernet/intel/i40e/i40e_main.c | 16 +++++++++++-----
> >  1 file changed, 11 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c
> > index 8f3b53e0dc46..f2ffa7ef74fd 100644
> > --- a/drivers/net/ethernet/intel/i40e/i40e_main.c
> > +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
> > @@ -7694,10 +7694,11 @@ 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;
> >  
> > @@ -7708,7 +7709,8 @@ 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);
> > @@ -7732,8 +7734,7 @@ 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)
> > @@ -7743,10 +7744,15 @@ 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;
> > 
> 
> 




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