Subject: Re: [Intel-wired-lan] [PATCH iwl-next v1] ice: lower default irq/queue counts on high-core systems

From: Michal Swiatkowski <[email-masked]>
Date: Fri, 17 Oct 2025 09:30:44 +0200

On Fri, Oct 17, 2025 at 07:03:31AM +0200, Przemek Kitszel wrote:
> On 10/16/25 17:36, Alexander Lobakin wrote:
> > From: Michal Swiatkowski <[email-masked]>
> > Date: Thu, 16 Oct 2025 08:22:50 +0200
> > 
> > > On some high-core systems 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 64 queues.
> > > Limit the default value to 64. Still, using ethtool the number of
> > > queues can be changed up to num_online_cpus().
> > > 
> > > This change affects only the default queue amount on systems with more
> > > than 64 cores.
> > > 
> > > Reviewed-by: Jacob Keller <[email-masked]>
> > > Signed-off-by: Michal Swiatkowski <[email-masked]>
> > > ---
> > >   drivers/net/ethernet/intel/ice/ice.h     | 20 ++++++++++++++++++++
> > >   drivers/net/ethernet/intel/ice/ice_irq.c |  6 ++++--
> > >   drivers/net/ethernet/intel/ice/ice_lib.c |  8 ++++----
> > >   3 files changed, 28 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/drivers/net/ethernet/intel/ice/ice.h b/drivers/net/ethernet/intel/ice/ice.h
> > > index 3d4d8b88631b..354ec2950ff3 100644
> > > --- a/drivers/net/ethernet/intel/ice/ice.h
> > > +++ b/drivers/net/ethernet/intel/ice/ice.h
> > > @@ -1133,4 +1133,24 @@ static inline struct ice_hw *ice_get_primary_hw(struct ice_pf *pf)
> > >   	else
> > >   		return &pf->adapter->ctrl_pf->hw;
> > >   }
> > > +
> > > +/**
> > > + * ice_capped_num_cpus - normalize the number of CPUs to a reasonable limit
> > > + *
> > > + * This function returns the number of online CPUs, but caps it at suitable
> > > + * default to prevent excessive resource allocation on systems with very high
> > > + * CPU counts.
> > > + *
> > > + * Note: suitable default is currently at 64, which is reflected in default_cpus
> > > + * constant. In most cases there is no much benefit for more than 64 and it is a
> > > + * power of 2 number.
> > > + *
> > > + * Return: number of online CPUs, capped at suitable default.
> > > + */
> > > +static inline u16 ice_capped_num_cpus(void)
> > > +{
> > > +	const int default_cpus = 64;
> > 
> > Maybe we should just use netif_get_num_default_rss_queues() like I did
> > in idpf?
> > 
> > Or it still can be too high e.g. on clusters with > 256 CPUs?
> 
> good point,
> perhaps we should both use it and change the (kernel) func to cap at 64
> 

Sounds good, thanks for pointing the function.

Do you think it is ok to cap the generic function? Maybe other vendors
want more default queues.

What about capping netif_get_num_default_rss_queues() at 64 just for
ice?

> > 
> > > +
> > > +	return min(num_online_cpus(), default_cpus);
> > > +}
> > >   #endif /* _ICE_H_ */
> > Thanks,
> > Olek
> > 
>