Subject: Re: [Intel-wired-lan] [PATCH iwl-next v2] ice: use netif_get_num_default_rss_queues()

From: Michal Swiatkowski <[email-masked]>
Date: Tue, 28 Oct 2025 10:08:24 +0100

On Tue, Oct 28, 2025 at 07:48:11AM +0000, Loktionov, Aleksandr wrote:
> 
> 
> > -----Original Message-----
> > From: Intel-wired-lan <[email-masked]> On Behalf
> > Of Michal Swiatkowski
> > Sent: Tuesday, October 28, 2025 8:07 AM
> > To: [email-masked]
> > Cc: [email-masked]; [email-masked]; Lobakin, Aleksander
> > <[email-masked]>; Kitszel, Przemyslaw
> > <[email-masked]>; Keller, Jacob E
> > <[email-masked]>; Michal Swiatkowski
> > <[email-masked]>
> > Subject: [Intel-wired-lan] [PATCH iwl-next v2] ice: use
> > netif_get_num_default_rss_queues()
> > 
> > On some high-core systems (like AMD EPYC Bergamo, Intel Clearwater
> > Forest) loading ice driver with default values can lead to queue/irq
> > exhaustion. It will result in no additional resources for SR-IOV.
> > 
> > In most cases there is no performance reason for more than half
> > num_cpus(). Limit the default value to it using generic
> > netif_get_num_default_rss_queues().
> > 
> > Still, using ethtool the number of queues can be changed up to
> > num_online_cpus(). It can be done by calling:
> > $ethtool -L ethX combined max_cpu
> > 
> It could be nice to use $(nproc)?
>  $ ethtool -L ethX combined $(nproc)

Will change

> 
> > This change affects only the default queue amount.
> > 
> > Signed-off-by: Michal Swiatkowski <[email-masked]>
> > ---
> > v1 --> v2:
> >  * Follow Olek's comment and switch from custom limiting to the
> > generic
> >    netif_...() function.
> >  * Add more info in commit message (Paul)
> >  * Dropping RB tags, as it is different patch now
> > ---
> >  drivers/net/ethernet/intel/ice/ice_irq.c |  5 +++--
> >  drivers/net/ethernet/intel/ice/ice_lib.c | 12 ++++++++----
> >  2 files changed, 11 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/intel/ice/ice_irq.c
> > b/drivers/net/ethernet/intel/ice/ice_irq.c
> > index 30801fd375f0..1d9b2d646474 100644
> > --- a/drivers/net/ethernet/intel/ice/ice_irq.c
> > +++ b/drivers/net/ethernet/intel/ice/ice_irq.c
> > @@ -106,9 +106,10 @@ static struct ice_irq_entry
> > *ice_get_irq_res(struct ice_pf *pf,
> >  #define ICE_RDMA_AEQ_MSIX 1
> >  static int ice_get_default_msix_amount(struct ice_pf *pf)
> >  {
> > -	return ICE_MIN_LAN_OICR_MSIX + num_online_cpus() +
> > +	return ICE_MIN_LAN_OICR_MSIX +
> > netif_get_num_default_rss_queues() +
> >  	       (test_bit(ICE_FLAG_FD_ENA, pf->flags) ? ICE_FDIR_MSIX :
> > 0) +
> > -	       (ice_is_rdma_ena(pf) ? num_online_cpus() +
> > ICE_RDMA_AEQ_MSIX : 0);
> > +	       (ice_is_rdma_ena(pf) ?
> > netif_get_num_default_rss_queues() +
> > +				      ICE_RDMA_AEQ_MSIX : 0);
> >  }
> > 
> >  /**
> > diff --git a/drivers/net/ethernet/intel/ice/ice_lib.c
> > b/drivers/net/ethernet/intel/ice/ice_lib.c
> > index bac481e8140d..e366d089bef9 100644
> > --- a/drivers/net/ethernet/intel/ice/ice_lib.c
> > +++ b/drivers/net/ethernet/intel/ice/ice_lib.c
> > @@ -159,12 +159,14 @@ static void ice_vsi_set_num_desc(struct ice_vsi
> > *vsi)
> > 
> >  static u16 ice_get_rxq_count(struct ice_pf *pf)
> >  {
> > -	return min(ice_get_avail_rxq_count(pf), num_online_cpus());
> > +	return min(ice_get_avail_rxq_count(pf),
> > +		   netif_get_num_default_rss_queues());
> >  }
> min(a, b) resolves to the type of the expression, which here will be int due to netif_get_num_default_rss_queues() returning int. 
> That implicitly truncates to u16 on return.
> What do you think about to make this explicit with min_t() to avoid type surprises?

We will just hide the truncing in the min_t() call. Probably if we
assuming that cpu / 2 can be higher than U16_MAX we should check that
here. Is it needed? (Previous situation is the same, num_online_cpus() is
returning int).

> 
> > 
> >  static u16 ice_get_txq_count(struct ice_pf *pf)
> >  {
> > -	return min(ice_get_avail_txq_count(pf), num_online_cpus());
> > +	return min(ice_get_avail_txq_count(pf),
> > +		   netif_get_num_default_rss_queues());
> >  }
> 
> Same min_t() ?
> 
> Otherwise, fine for me.

Thanks

> 
> Reviewed-by: Aleksandr Loktionov <[email-masked]>