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: Wed, 22 Oct 2025 09:09:42 +0200

On Fri, Oct 17, 2025 at 04:35:18PM +0200, Alexander Lobakin wrote:
> 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.
> 
> Nah I don't think it's a good idea to hardcode any numbers in the
> generic function.
> 
> > 
> > What about capping netif_get_num_default_rss_queues() at 64 just for
> > ice?
> 
> netif_get_num_default_rss_queues() returns *half* of the number of
> *physical* cores. I.e. it will return something bigger than 64 only in
> case of > 256 threads in the system (considering SMT).
> 
> Do we need to still cap this to 64 in ice at all?

That can be good enough. I will send next version with just call to this
function.

> Thanks,
> Olek