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

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Message-ID: <5d739d1f-faa7-4734-b5e7-8e35b5556ce7@intel.com>
Date: Thu, 16 Oct 2025 17:36:21 +0200
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
CC: <intel-wired-lan@...ts.osuosl.org>, <netdev@...r.kernel.org>, Jacob Keller
	<jacob.e.keller@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH iwl-next v1] ice: lower default
 irq/queue counts on high-core systems

From: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
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 <jacob.e.keller@...el.com>
> Signed-off-by: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
> ---
>  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?

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